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|
/*
* Read-Copy Update mechanism for mutual exclusion
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, you can access it online at
* http://www.gnu.org/licenses/gpl-2.0.html.
*
* Copyright IBM Corporation, 2008
*
* Authors: Dipankar Sarma <dipankar@in.ibm.com>
* Manfred Spraul <manfred@colorfullife.com>
* Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
*
* Based on the original work by Paul McKenney <paulmck@us.ibm.com>
* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
*
* For detailed explanation of Read-Copy Update mechanism see -
* Documentation/RCU
*/
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/rcupdate_wait.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/nmi.h>
#include <linux/atomic.h>
#include <linux/bitops.h>
#include <linux/export.h>
#include <linux/completion.h>
#include <linux/moduleparam.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>
#include <linux/time.h>
#include <linux/kernel_stat.h>
#include <linux/wait.h>
#include <linux/kthread.h>
#include <uapi/linux/sched/types.h>
#include <linux/prefetch.h>
#include <linux/delay.h>
#include <linux/stop_machine.h>
#include <linux/random.h>
#include <linux/trace_events.h>
#include <linux/suspend.h>
#include "tree.h"
#include "rcu.h"
#ifdef MODULE_PARAM_PREFIX
#undef MODULE_PARAM_PREFIX
#endif
#define MODULE_PARAM_PREFIX "rcutree."
/* Data structures. */
/*
* In order to export the rcu_state name to the tracing tools, it
* needs to be added in the __tracepoint_string section.
* This requires defining a separate variable tp_<sname>_varname
* that points to the string being used, and this will allow
* the tracing userspace tools to be able to decipher the string
* address to the matching string.
*/
#ifdef CONFIG_TRACING
# define DEFINE_RCU_TPS(sname) \
static char sname##_varname[] = #sname; \
static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname;
# define RCU_STATE_NAME(sname) sname##_varname
#else
# define DEFINE_RCU_TPS(sname)
# define RCU_STATE_NAME(sname) __stringify(sname)
#endif
#define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
DEFINE_RCU_TPS(sname) \
static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data); \
struct rcu_state sname##_state = { \
.level = { &sname##_state.node[0] }, \
.rda = &sname##_data, \
.call = cr, \
.gp_state = RCU_GP_IDLE, \
.gpnum = 0UL - 300UL, \
.completed = 0UL - 300UL, \
.orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
.orphan_pend = RCU_CBLIST_INITIALIZER(sname##_state.orphan_pend), \
.orphan_done = RCU_CBLIST_INITIALIZER(sname##_state.orphan_done), \
.barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
.name = RCU_STATE_NAME(sname), \
.abbr = sabbr, \
.exp_mutex = __MUTEX_INITIALIZER(sname##_state.exp_mutex), \
.exp_wake_mutex = __MUTEX_INITIALIZER(sname##_state.exp_wake_mutex), \
}
RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
static struct rcu_state *const rcu_state_p;
LIST_HEAD(rcu_struct_flavors);
/* Dump rcu_node combining tree at boot to verify correct setup. */
static bool dump_tree;
module_param(dump_tree, bool, 0444);
/* Control rcu_node-tree auto-balancing at boot time. */
static bool rcu_fanout_exact;
module_param(rcu_fanout_exact, bool, 0444);
/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
module_param(rcu_fanout_leaf, int, 0444);
int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
/* Number of rcu_nodes at specified level. */
static int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
/* panic() on RCU Stall sysctl. */
int sysctl_panic_on_rcu_stall __read_mostly;
/*
* The rcu_scheduler_active variable is initialized to the value
* RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the
* first task is spawned. So when this variable is RCU_SCHEDULER_INACTIVE,
* RCU can assume that there is but one task, allowing RCU to (for example)
* optimize synchronize_rcu() to a simple barrier(). When this variable
* is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required
* to detect real grace periods. This variable is also used to suppress
* boot-time false positives from lockdep-RCU error checking. Finally, it
* transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU
* is fully initialized, including all of its kthreads having been spawned.
*/
int rcu_scheduler_active __read_mostly;
EXPORT_SYMBOL_GPL(rcu_scheduler_active);
/*
* The rcu_scheduler_fully_active variable transitions from zero to one
* during the early_initcall() processing, which is after the scheduler
* is capable of creating new tasks. So RCU processing (for example,
* creating tasks for RCU priority boosting) must be delayed until after
* rcu_scheduler_fully_active transitions from zero to one. We also
* currently delay invocation of any RCU callbacks until after this point.
*
* It might later prove better for people registering RCU callbacks during
* early boot to take responsibility for these callbacks, but one step at
* a time.
*/
static int rcu_scheduler_fully_active __read_mostly;
static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
static void invoke_rcu_core(void);
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
static void rcu_report_exp_rdp(struct rcu_state *rsp,
struct rcu_data *rdp, bool wake);
static void sync_sched_exp_online_cleanup(int cpu);
/* rcuc/rcub kthread realtime priority */
#ifdef CONFIG_RCU_KTHREAD_PRIO
static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO;
#else /* #ifdef CONFIG_RCU_KTHREAD_PRIO */
static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
#endif /* #else #ifdef CONFIG_RCU_KTHREAD_PRIO */
module_param(kthread_prio, int, 0644);
/* Delay in jiffies for grace-period initialization delays, debug only. */
#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT
static int gp_preinit_delay = CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT_DELAY;
module_param(gp_preinit_delay, int, 0644);
#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT */
static const int gp_preinit_delay;
#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT */
#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT
static int gp_init_delay = CONFIG_RCU_TORTURE_TEST_SLOW_INIT_DELAY;
module_param(gp_init_delay, int, 0644);
#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */
static const int gp_init_delay;
#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */
#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP
static int gp_cleanup_delay = CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP_DELAY;
module_param(gp_cleanup_delay, int, 0644);
#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP */
static const int gp_cleanup_delay;
#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP */
/*
* Number of grace periods between delays, normalized by the duration of
* the delay. The longer the the delay, the more the grace periods between
* each delay. The reason for this normalization is that it means that,
* for non-zero delays, the overall slowdown of grace periods is constant
* regardless of the duration of the delay. This arrangement balances
* the need for long delays to increase some race probabilities with the
* need for fast grace periods to increase other race probabilities.
*/
#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays. */
/*
* Track the rcutorture test sequence number and the update version
* number within a given test. The rcutorture_testseq is incremented
* on every rcutorture module load and unload, so has an odd value
* when a test is running. The rcutorture_vernum is set to zero
* when rcutorture starts and is incremented on each rcutorture update.
* These variables enable correlating rcutorture output with the
* RCU tracing information.
*/
unsigned long rcutorture_testseq;
unsigned long rcutorture_vernum;
/*
* Compute the mask of online CPUs for the specified rcu_node structure.
* This will not be stable unless the rcu_node structure's ->lock is
* held, but the bit corresponding to the current CPU will be stable
* in most contexts.
*/
unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
{
return READ_ONCE(rnp->qsmaskinitnext);
}
/*
* Return true if an RCU grace period is in progress. The READ_ONCE()s
* permit this function to be invoked without holding the root rcu_node
* structure's ->lock, but of course results can be subject to change.
*/
static int rcu_gp_in_progress(struct rcu_state *rsp)
{
return READ_ONCE(rsp->completed) != READ_ONCE(rsp->gpnum);
}
/*
* Note a quiescent state. Because we do not need to know
* how many quiescent states passed, just if there was at least
* one since the start of the grace period, this just sets a flag.
* The caller must have disabled preemption.
*/
void rcu_sched_qs(void)
{
if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.s))
return;
trace_rcu_grace_period(TPS("rcu_sched"),
__this_cpu_read(rcu_sched_data.gpnum),
TPS("cpuqs"));
__this_cpu_write(rcu_sched_data.cpu_no_qs.b.norm, false);
if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
return;
__this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, false);
rcu_report_exp_rdp(&rcu_sched_state,
this_cpu_ptr(&rcu_sched_data), true);
}
void rcu_bh_qs(void)
{
if (__this_cpu_read(rcu_bh_data.cpu_no_qs.s)) {
trace_rcu_grace_period(TPS("rcu_bh"),
__this_cpu_read(rcu_bh_data.gpnum),
TPS("cpuqs"));
__this_cpu_write(rcu_bh_data.cpu_no_qs.b.norm, false);
}
}
/*
* Steal a bit from the bottom of ->dynticks for idle entry/exit
* control. Initially this is for TLB flushing.
*/
#define RCU_DYNTICK_CTRL_MASK 0x1
#define RCU_DYNTICK_CTRL_CTR (RCU_DYNTICK_CTRL_MASK + 1)
#ifndef rcu_eqs_special_exit
#define rcu_eqs_special_exit() do { } while (0)
#endif
static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
.dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
.dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),
#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
.dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE,
.dynticks_idle = ATOMIC_INIT(1),
#endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
};
/*
* Record entry into an extended quiescent state. This is only to be
* called when not already in an extended quiescent state.
*/
static void rcu_dynticks_eqs_enter(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
int seq;
/*
* CPUs seeing atomic_add_return() must see prior RCU read-side
* critical sections, and we also must force ordering with the
* next idle sojourn.
*/
seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
/* Better be in an extended quiescent state! */
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
(seq & RCU_DYNTICK_CTRL_CTR));
/* Better not have special action (TLB flush) pending! */
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
(seq & RCU_DYNTICK_CTRL_MASK));
}
/*
* Record exit from an extended quiescent state. This is only to be
* called from an extended quiescent state.
*/
static void rcu_dynticks_eqs_exit(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
int seq;
/*
* CPUs seeing atomic_add_return() must see prior idle sojourns,
* and we also must force ordering with the next RCU read-side
* critical section.
*/
seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
!(seq & RCU_DYNTICK_CTRL_CTR));
if (seq & RCU_DYNTICK_CTRL_MASK) {
atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdtp->dynticks);
smp_mb__after_atomic(); /* _exit after clearing mask. */
/* Prefer duplicate flushes to losing a flush. */
rcu_eqs_special_exit();
}
}
/*
* Reset the current CPU's ->dynticks counter to indicate that the
* newly onlined CPU is no longer in an extended quiescent state.
* This will either leave the counter unchanged, or increment it
* to the next non-quiescent value.
*
* The non-atomic test/increment sequence works because the upper bits
* of the ->dynticks counter are manipulated only by the corresponding CPU,
* or when the corresponding CPU is offline.
*/
static void rcu_dynticks_eqs_online(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
if (atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR)
return;
atomic_add(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
}
/*
* Is the current CPU in an extended quiescent state?
*
* No ordering, as we are sampling CPU-local information.
*/
bool rcu_dynticks_curr_cpu_in_eqs(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
return !(atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR);
}
/*
* Snapshot the ->dynticks counter with full ordering so as to allow
* stable comparison of this counter with past and future snapshots.
*/
int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
{
int snap = atomic_add_return(0, &rdtp->dynticks);
return snap & ~RCU_DYNTICK_CTRL_MASK;
}
/*
* Return true if the snapshot returned from rcu_dynticks_snap()
* indicates that RCU is in an extended quiescent state.
*/
static bool rcu_dynticks_in_eqs(int snap)
{
return !(snap & RCU_DYNTICK_CTRL_CTR);
}
/*
* Return true if the CPU corresponding to the specified rcu_dynticks
* structure has spent some time in an extended quiescent state since
* rcu_dynticks_snap() returned the specified snapshot.
*/
static bool rcu_dynticks_in_eqs_since(struct rcu_dynticks *rdtp, int snap)
{
return snap != rcu_dynticks_snap(rdtp);
}
/*
* Do a double-increment of the ->dynticks counter to emulate a
* momentary idle-CPU quiescent state.
*/
static void rcu_dynticks_momentary_idle(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
int special = atomic_add_return(2 * RCU_DYNTICK_CTRL_CTR,
&rdtp->dynticks);
/* It is illegal to call this from idle state. */
WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR));
}
/*
* Set the special (bottom) bit of the specified CPU so that it
* will take special action (such as flushing its TLB) on the
* next exit from an extended quiescent state. Returns true if
* the bit was successfully set, or false if the CPU was not in
* an extended quiescent state.
*/
bool rcu_eqs_special_set(int cpu)
{
int old;
int new;
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
do {
old = atomic_read(&rdtp->dynticks);
if (old & RCU_DYNTICK_CTRL_CTR)
return false;
new = old | RCU_DYNTICK_CTRL_MASK;
} while (atomic_cmpxchg(&rdtp->dynticks, old, new) != old);
return true;
}
/*
* Let the RCU core know that this CPU has gone through the scheduler,
* which is a quiescent state. This is called when the need for a
* quiescent state is urgent, so we burn an atomic operation and full
* memory barriers to let the RCU core know about it, regardless of what
* this CPU might (or might not) do in the near future.
*
* We inform the RCU core by emulating a zero-duration dyntick-idle period.
*
* The caller must have disabled interrupts.
*/
static void rcu_momentary_dyntick_idle(void)
{
raw_cpu_write(rcu_dynticks.rcu_need_heavy_qs, false);
rcu_dynticks_momentary_idle();
}
/*
* Note a context switch. This is a quiescent state for RCU-sched,
* and requires special handling for preemptible RCU.
* The caller must have disabled interrupts.
*/
void rcu_note_context_switch(void)
{
barrier(); /* Avoid RCU read-side critical sections leaking down. */
trace_rcu_utilization(TPS("Start context switch"));
rcu_sched_qs();
rcu_preempt_note_context_switch();
/* Load rcu_urgent_qs before other flags. */
if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs)))
goto out;
this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs)))
rcu_momentary_dyntick_idle();
this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
out:
trace_rcu_utilization(TPS("End context switch"));
barrier(); /* Avoid RCU read-side critical sections leaking up. */
}
EXPORT_SYMBOL_GPL(rcu_note_context_switch);
/*
* Register a quiescent state for all RCU flavors. If there is an
* emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
* dyntick-idle quiescent state visible to other CPUs (but only for those
* RCU flavors in desperate need of a quiescent state, which will normally
* be none of them). Either way, do a lightweight quiescent state for
* all RCU flavors.
*
* The barrier() calls are redundant in the common case when this is
* called externally, but just in case this is called from within this
* file.
*
*/
void rcu_all_qs(void)
{
unsigned long flags;
if (!raw_cpu_read(rcu_dynticks.rcu_urgent_qs))
return;
preempt_disable();
/* Load rcu_urgent_qs before other flags. */
if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) {
preempt_enable();
return;
}
this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
barrier(); /* Avoid RCU read-side critical sections leaking down. */
if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) {
local_irq_save(flags);
rcu_momentary_dyntick_idle();
local_irq_restore(flags);
}
if (unlikely(raw_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)))
rcu_sched_qs();
this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
barrier(); /* Avoid RCU read-side critical sections leaking up. */
preempt_enable();
}
EXPORT_SYMBOL_GPL(rcu_all_qs);
static long blimit = 10; /* Maximum callbacks per rcu_do_batch. */
static long qhimark = 10000; /* If this many pending, ignore blimit. */
static long qlowmark = 100; /* Once only this many pending, use blimit. */
module_param(blimit, long, 0444);
module_param(qhimark, long, 0444);
module_param(qlowmark, long, 0444);
static ulong jiffies_till_first_fqs = ULONG_MAX;
static ulong jiffies_till_next_fqs = ULONG_MAX;
static bool rcu_kick_kthreads;
module_param(jiffies_till_first_fqs, ulong, 0644);
module_param(jiffies_till_next_fqs, ulong, 0644);
module_param(rcu_kick_kthreads, bool, 0644);
/*
* How long the grace period must be before we start recruiting
* quiescent-state help from rcu_note_context_switch().
*/
static ulong jiffies_till_sched_qs = HZ / 20;
module_param(jiffies_till_sched_qs, ulong, 0644);
static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
struct rcu_data *rdp);
static void force_qs_rnp(struct rcu_state *rsp,
int (*f)(struct rcu_data *rsp, bool *isidle,
unsigned long *maxj),
bool *isidle, unsigned long *maxj);
static void force_quiescent_state(struct rcu_state *rsp);
static int rcu_pending(void);
/*
* Return the number of RCU batches started thus far for debug & stats.
*/
unsigned long rcu_batches_started(void)
{
return rcu_state_p->gpnum;
}
EXPORT_SYMBOL_GPL(rcu_batches_started);
/*
* Return the number of RCU-sched batches started thus far for debug & stats.
*/
unsigned long rcu_batches_started_sched(void)
{
return rcu_sched_state.gpnum;
}
EXPORT_SYMBOL_GPL(rcu_batches_started_sched);
/*
* Return the number of RCU BH batches started thus far for debug & stats.
*/
unsigned long rcu_batches_started_bh(void)
{
return rcu_bh_state.gpnum;
}
EXPORT_SYMBOL_GPL(rcu_batches_started_bh);
/*
* Return the number of RCU batches completed thus far for debug & stats.
*/
unsigned long rcu_batches_completed(void)
{
return rcu_state_p->completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed);
/*
* Return the number of RCU-sched batches completed thus far for debug & stats.
*/
unsigned long rcu_batches_completed_sched(void)
{
return rcu_sched_state.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
/*
* Return the number of RCU BH batches completed thus far for debug & stats.
*/
unsigned long rcu_batches_completed_bh(void)
{
return rcu_bh_state.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
/*
* Return the number of RCU expedited batches completed thus far for
* debug & stats. Odd numbers mean that a batch is in progress, even
* numbers mean idle. The value returned will thus be roughly double
* the cumulative batches since boot.
*/
unsigned long rcu_exp_batches_completed(void)
{
return rcu_state_p->expedited_sequence;
}
EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
/*
* Return the number of RCU-sched expedited batches completed thus far
* for debug & stats. Similar to rcu_exp_batches_completed().
*/
unsigned long rcu_exp_batches_completed_sched(void)
{
return rcu_sched_state.expedited_sequence;
}
EXPORT_SYMBOL_GPL(rcu_exp_batches_completed_sched);
/*
* Force a quiescent state.
*/
void rcu_force_quiescent_state(void)
{
force_quiescent_state(rcu_state_p);
}
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
/*
* Force a quiescent state for RCU BH.
*/
void rcu_bh_force_quiescent_state(void)
{
force_quiescent_state(&rcu_bh_state);
}
EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
/*
* Force a quiescent state for RCU-sched.
*/
void rcu_sched_force_quiescent_state(void)
{
force_quiescent_state(&rcu_sched_state);
}
EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
/*
* Show the state of the grace-period kthreads.
*/
void show_rcu_gp_kthreads(void)
{
struct rcu_state *rsp;
for_each_rcu_flavor(rsp) {
pr_info("%s: wait state: %d ->state: %#lx\n",
rsp->name, rsp->gp_state, rsp->gp_kthread->state);
/* sched_show_task(rsp->gp_kthread); */
}
}
EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
/*
* Record the number of times rcutorture tests have been initiated and
* terminated. This information allows the debugfs tracing stats to be
* correlated to the rcutorture messages, even when the rcutorture module
* is being repeatedly loaded and unloaded. In other words, we cannot
* store this state in rcutorture itself.
*/
void rcutorture_record_test_transition(void)
{
rcutorture_testseq++;
rcutorture_vernum = 0;
}
EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);
/*
* Send along grace-period-related data for rcutorture diagnostics.
*/
void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
unsigned long *gpnum, unsigned long *completed)
{
struct rcu_state *rsp = NULL;
switch (test_type) {
case RCU_FLAVOR:
rsp = rcu_state_p;
break;
case RCU_BH_FLAVOR:
rsp = &rcu_bh_state;
break;
case RCU_SCHED_FLAVOR:
rsp = &rcu_sched_state;
break;
default:
break;
}
if (rsp != NULL) {
*flags = READ_ONCE(rsp->gp_flags);
*gpnum = READ_ONCE(rsp->gpnum);
*completed = READ_ONCE(rsp->completed);
return;
}
*flags = 0;
*gpnum = 0;
*completed = 0;
}
EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
/*
* Record the number of writer passes through the current rcutorture test.
* This is also used to correlate debugfs tracing stats with the rcutorture
* messages.
*/
void rcutorture_record_progress(unsigned long vernum)
{
rcutorture_vernum++;
}
EXPORT_SYMBOL_GPL(rcutorture_record_progress);
/*
* Return the root node of the specified rcu_state structure.
*/
static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
{
return &rsp->node[0];
}
/*
* Is there any need for future grace periods?
* Interrupts must be disabled. If the caller does not hold the root
* rnp_node structure's ->lock, the results are advisory only.
*/
static int rcu_future_needs_gp(struct rcu_state *rsp)
{
struct rcu_node *rnp = rcu_get_root(rsp);
int idx = (READ_ONCE(rnp->completed) + 1) & 0x1;
int *fp = &rnp->need_future_gp[idx];
return READ_ONCE(*fp);
}
/*
* Does the current CPU require a not-yet-started grace period?
* The caller must have disabled interrupts to prevent races with
* normal callback registry.
*/
static bool
cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
{
if (rcu_gp_in_progress(rsp))
return false; /* No, a grace period is already in progress. */
if (rcu_future_needs_gp(rsp))
return true; /* Yes, a no-CBs CPU needs one. */
if (!rcu_segcblist_is_enabled(&rdp->cblist))
return false; /* No, this is a no-CBs (or offline) CPU. */
if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
return true; /* Yes, CPU has newly registered callbacks. */
if (rcu_segcblist_future_gp_needed(&rdp->cblist,
READ_ONCE(rsp->completed)))
return true; /* Yes, CBs for future grace period. */
return false; /* No grace period needed. */
}
/*
* rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
*
* If the new value of the ->dynticks_nesting counter now is zero,
* we really have entered idle, and must do the appropriate accounting.
* The caller must have disabled interrupts.
*/
static void rcu_eqs_enter_common(long long oldval, bool user)
{
struct rcu_state *rsp;
struct rcu_data *rdp;
RCU_TRACE(struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);)
trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
!user && !is_idle_task(current)) {
struct task_struct *idle __maybe_unused =
idle_task(smp_processor_id());
trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval, 0);
rcu_ftrace_dump(DUMP_ORIG);
WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
current->pid, current->comm,
idle->pid, idle->comm); /* must be idle task! */
}
for_each_rcu_flavor(rsp) {
rdp = this_cpu_ptr(rsp->rda);
do_nocb_deferred_wakeup(rdp);
}
rcu_prepare_for_idle();
rcu_dynticks_eqs_enter();
rcu_dynticks_task_enter();
/*
* It is illegal to enter an extended quiescent state while
* in an RCU read-side critical section.
*/
RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
"Illegal idle entry in RCU read-side critical section.");
RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map),
"Illegal idle entry in RCU-bh read-side critical section.");
RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map),
"Illegal idle entry in RCU-sched read-side critical section.");
}
/*
* Enter an RCU extended quiescent state, which can be either the
* idle loop or adaptive-tickless usermode execution.
*/
static void rcu_eqs_enter(bool user)
{
long long oldval;
struct rcu_dynticks *rdtp;
rdtp = this_cpu_ptr(&rcu_dynticks);
oldval = rdtp->dynticks_nesting;
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
(oldval & DYNTICK_TASK_NEST_MASK) == 0);
if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) {
rdtp->dynticks_nesting = 0;
rcu_eqs_enter_common(oldval, user);
} else {
rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
}
}
/**
* rcu_idle_enter - inform RCU that current CPU is entering idle
*
* Enter idle mode, in other words, -leave- the mode in which RCU
* read-side critical sections can occur. (Though RCU read-side
* critical sections can occur in irq handlers in idle, a possibility
* handled by irq_enter() and irq_exit().)
*
* We crowbar the ->dynticks_nesting field to zero to allow for
* the possibility of usermode upcalls having messed up our count
* of interrupt nesting level during the prior busy period.
*/
void rcu_idle_enter(void)
{
unsigned long flags;
local_irq_save(flags);
rcu_eqs_enter(false);
rcu_sysidle_enter(0);
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_enter);
#ifdef CONFIG_NO_HZ_FULL
/**
* rcu_user_enter - inform RCU that we are resuming userspace.
*
* Enter RCU idle mode right before resuming userspace. No use of RCU
* is permitted between this call and rcu_user_exit(). This way the
* CPU doesn't need to maintain the tick for RCU maintenance purposes
* when the CPU runs in userspace.
*/
void rcu_user_enter(void)
{
rcu_eqs_enter(1);
}
#endif /* CONFIG_NO_HZ_FULL */
/**
* rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
*
* Exit from an interrupt handler, which might possibly result in entering
* idle mode, in other words, leaving the mode in which read-side critical
* sections can occur. The caller must have disabled interrupts.
*
* This code assumes that the idle loop never does anything that might
* result in unbalanced calls to irq_enter() and irq_exit(). If your
* architecture violates this assumption, RCU will give you what you
* deserve, good and hard. But very infrequently and irreproducibly.
*
* Use things like work queues to work around this limitation.
*
* You have been warned.
*/
void rcu_irq_exit(void)
{
long long oldval;
struct rcu_dynticks *rdtp;
RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_exit() invoked with irqs enabled!!!");
rdtp = this_cpu_ptr(&rcu_dynticks);
oldval = rdtp->dynticks_nesting;
rdtp->dynticks_nesting--;
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
rdtp->dynticks_nesting < 0);
if (rdtp->dynticks_nesting)
trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
else
rcu_eqs_enter_common(oldval, true);
rcu_sysidle_enter(1);
}
/*
* Wrapper for rcu_irq_exit() where interrupts are enabled.
*/
void rcu_irq_exit_irqson(void)
{
unsigned long flags;
local_irq_save(flags);
rcu_irq_exit();
local_irq_restore(flags);
}
/*
* rcu_eqs_exit_common - current CPU moving away from extended quiescent state
*
* If the new value of the ->dynticks_nesting counter was previously zero,
* we really have exited idle, and must do the appropriate accounting.
* The caller must have disabled interrupts.
*/
static void rcu_eqs_exit_common(long long oldval, int user)
{
RCU_TRACE(struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);)
rcu_dynticks_task_exit();
rcu_dynticks_eqs_exit();
rcu_cleanup_after_idle();
trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
!user && !is_idle_task(current)) {
struct task_struct *idle __maybe_unused =
idle_task(smp_processor_id());
trace_rcu_dyntick(TPS("Error on exit: not idle task"),
oldval, rdtp->dynticks_nesting);
rcu_ftrace_dump(DUMP_ORIG);
WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
current->pid, current->comm,
idle->pid, idle->comm); /* must be idle task! */
}
}
/*
* Exit an RCU extended quiescent state, which can be either the
* idle loop or adaptive-tickless usermode execution.
*/
static void rcu_eqs_exit(bool user)
{
struct rcu_dynticks *rdtp;
long long oldval;
rdtp = this_cpu_ptr(&rcu_dynticks);
oldval = rdtp->dynticks_nesting;
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
if (oldval & DYNTICK_TASK_NEST_MASK) {
rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
} else {
rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
rcu_eqs_exit_common(oldval, user);
}
}
/**
* rcu_idle_exit - inform RCU that current CPU is leaving idle
*
* Exit idle mode, in other words, -enter- the mode in which RCU
* read-side critical sections can occur.
*
* We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
* allow for the possibility of usermode upcalls messing up our count
* of interrupt nesting level during the busy period that is just
* now starting.
*/
void rcu_idle_exit(void)
{
unsigned long flags;
local_irq_save(flags);
rcu_eqs_exit(false);
rcu_sysidle_exit(0);
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(rcu_idle_exit);
#ifdef CONFIG_NO_HZ_FULL
/**
* rcu_user_exit - inform RCU that we are exiting userspace.
*
* Exit RCU idle mode while entering the kernel because it can
* run a RCU read side critical section anytime.
*/
void rcu_user_exit(void)
{
rcu_eqs_exit(1);
}
#endif /* CONFIG_NO_HZ_FULL */
/**
* rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
*
* Enter an interrupt handler, which might possibly result in exiting
* idle mode, in other words, entering the mode in which read-side critical
* sections can occur. The caller must have disabled interrupts.
*
* Note that the Linux kernel is fully capable of entering an interrupt
* handler that it never exits, for example when doing upcalls to
* user mode! This code assumes that the idle loop never does upcalls to
* user mode. If your architecture does do upcalls from the idle loop (or
* does anything else that results in unbalanced calls to the irq_enter()
* and irq_exit() functions), RCU will give you what you deserve, good
* and hard. But very infrequently and irreproducibly.
*
* Use things like work queues to work around this limitation.
*
* You have been warned.
*/
void rcu_irq_enter(void)
{
struct rcu_dynticks *rdtp;
long long oldval;
RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_enter() invoked with irqs enabled!!!");
rdtp = this_cpu_ptr(&rcu_dynticks);
oldval = rdtp->dynticks_nesting;
rdtp->dynticks_nesting++;
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
rdtp->dynticks_nesting == 0);
if (oldval)
trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
else
rcu_eqs_exit_common(oldval, true);
rcu_sysidle_exit(1);
}
/*
* Wrapper for rcu_irq_enter() where interrupts are enabled.
*/
void rcu_irq_enter_irqson(void)
{
unsigned long flags;
local_irq_save(flags);
rcu_irq_enter();
local_irq_restore(flags);
}
/**
* rcu_nmi_enter - inform RCU of entry to NMI context
*
* If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and
* rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know
* that the CPU is active. This implementation permits nested NMIs, as
* long as the nesting level does not overflow an int. (You will probably
* run out of stack space first.)
*/
void rcu_nmi_enter(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
int incby = 2;
/* Complain about underflow. */
WARN_ON_ONCE(rdtp->dynticks_nmi_nesting < 0);
/*
* If idle from RCU viewpoint, atomically increment ->dynticks
* to mark non-idle and increment ->dynticks_nmi_nesting by one.
* Otherwise, increment ->dynticks_nmi_nesting by two. This means
* if ->dynticks_nmi_nesting is equal to one, we are guaranteed
* to be in the outermost NMI handler that interrupted an RCU-idle
* period (observation due to Andy Lutomirski).
*/
if (rcu_dynticks_curr_cpu_in_eqs()) {
rcu_dynticks_eqs_exit();
incby = 1;
}
rdtp->dynticks_nmi_nesting += incby;
barrier();
}
/**
* rcu_nmi_exit - inform RCU of exit from NMI context
*
* If we are returning from the outermost NMI handler that interrupted an
* RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting
* to let the RCU grace-period handling know that the CPU is back to
* being RCU-idle.
*/
void rcu_nmi_exit(void)
{
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
/*
* Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
* (We are exiting an NMI handler, so RCU better be paying attention
* to us!)
*/
WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0);
WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs());
/*
* If the nesting level is not 1, the CPU wasn't RCU-idle, so
* leave it in non-RCU-idle state.
*/
if (rdtp->dynticks_nmi_nesting != 1) {
rdtp->dynticks_nmi_nesting -= 2;
return;
}
/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
rdtp->dynticks_nmi_nesting = 0;
rcu_dynticks_eqs_enter();
}
/**
* __rcu_is_watching - are RCU read-side critical sections safe?
*
* Return true if RCU is watching the running CPU, which means that
* this CPU can safely enter RCU read-side critical sections. Unlike
* rcu_is_watching(), the caller of __rcu_is_watching() must have at
* least disabled preemption.
*/
bool notrace __rcu_is_watching(void)
{
return !rcu_dynticks_curr_cpu_in_eqs();
}
/**
* rcu_is_watching - see if RCU thinks that the current CPU is idle
*
* If the current CPU is in its idle loop and is neither in an interrupt
* or NMI handler, return true.
*/
bool notrace rcu_is_watching(void)
{
bool ret;
preempt_disable_notrace();
ret = __rcu_is_watching();
preempt_enable_notrace();
return ret;
}
EXPORT_SYMBOL_GPL(rcu_is_watching);
#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
/*
* Is the current CPU online? Disable preemption to avoid false positives
* that could otherwise happen due to the current CPU number being sampled,
* this task being preempted, its old CPU being taken offline, resuming
* on some other CPU, then determining that its old CPU is now offline.
* It is OK to use RCU on an offline processor during initial boot, hence
* the check for rcu_scheduler_fully_active. Note also that it is OK
* for a CPU coming online to use RCU for one jiffy prior to marking itself
* online in the cpu_online_mask. Similarly, it is OK for a CPU going
* offline to continue to use RCU for one jiffy after marking itself
* offline in the cpu_online_mask. This leniency is necessary given the
* non-atomic nature of the online and offline processing, for example,
* the fact that a CPU enters the scheduler after completing the teardown
* of the CPU.
*
* This is also why RCU internally marks CPUs online during in the
* preparation phase and offline after the CPU has been taken down.
*
* Disable checking if in an NMI handler because we cannot safely report
* errors from NMI handlers anyway.
*/
bool rcu_lockdep_current_cpu_online(void)
{
struct rcu_data *rdp;
struct rcu_node *rnp;
bool ret;
if (in_nmi())
return true;
preempt_disable();
rdp = this_cpu_ptr(&rcu_sched_data);
rnp = rdp->mynode;
ret = (rdp->grpmask & rcu_rnp_online_cpus(rnp)) ||
!rcu_scheduler_fully_active;
preempt_enable();
return ret;
}
EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
/**
* rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
*
* If the current CPU is idle or running at a first-level (not nested)
* interrupt from idle, return true. The caller must have at least
* disabled preemption.
*/
static int rcu_is_cpu_rrupt_from_idle(void)
{
return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
}
/*
* Snapshot the specified CPU's dynticks counter so that we can later
* credit them with an implicit quiescent state. Return 1 if this CPU
* is in dynticks idle mode, which is an extended quiescent state.
*/
static int dyntick_save_progress_counter(struct rcu_data *rdp,
bool *isidle, unsigned long *maxj)
{
rdp->dynticks_snap = rcu_dynticks_snap(rdp->dynticks);
rcu_sysidle_check_cpu(rdp, isidle, maxj);
if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4,
rdp->mynode->gpnum))
WRITE_ONCE(rdp->gpwrap, true);
return 1;
}
return 0;
}
/*
* Return true if the specified CPU has passed through a quiescent
* state by virtue of being in or having passed through an dynticks
* idle state since the last call to dyntick_save_progress_counter()
* for this same CPU, or by virtue of having been offline.
*/
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
bool *isidle, unsigned long *maxj)
{
unsigned long jtsq;
bool *rnhqp;
bool *ruqp;
unsigned long rjtsc;
struct rcu_node *rnp;
/*
* If the CPU passed through or entered a dynticks idle phase with
* no active irq/NMI handlers, then we can safely pretend that the CPU
* already acknowledged the request to pass through a quiescent
* state. Either way, that CPU cannot possibly be in an RCU
* read-side critical section that started before the beginning
* of the current RCU grace period.
*/
if (rcu_dynticks_in_eqs_since(rdp->dynticks, rdp->dynticks_snap)) {
trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
rdp->dynticks_fqs++;
return 1;
}
/* Compute and saturate jiffies_till_sched_qs. */
jtsq = jiffies_till_sched_qs;
rjtsc = rcu_jiffies_till_stall_check();
if (jtsq > rjtsc / 2) {
WRITE_ONCE(jiffies_till_sched_qs, rjtsc);
jtsq = rjtsc / 2;
} else if (jtsq < 1) {
WRITE_ONCE(jiffies_till_sched_qs, 1);
jtsq = 1;
}
/*
* Has this CPU encountered a cond_resched_rcu_qs() since the
* beginning of the grace period? For this to be the case,
* the CPU has to have noticed the current grace period. This
* might not be the case for nohz_full CPUs looping in the kernel.
*/
rnp = rdp->mynode;
ruqp = per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, rdp->cpu);
if (time_after(jiffies, rdp->rsp->gp_start + jtsq) &&
READ_ONCE(rdp->rcu_qs_ctr_snap) != per_cpu(rcu_dynticks.rcu_qs_ctr, rdp->cpu) &&
READ_ONCE(rdp->gpnum) == rnp->gpnum && !rdp->gpwrap) {
trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("rqc"));
return 1;
} else {
/* Load rcu_qs_ctr before store to rcu_urgent_qs. */
smp_store_release(ruqp, true);
}
/* Check for the CPU being offline. */
if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp))) {
trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
rdp->offline_fqs++;
return 1;
}
/*
* A CPU running for an extended time within the kernel can
* delay RCU grace periods. When the CPU is in NO_HZ_FULL mode,
* even context-switching back and forth between a pair of
* in-kernel CPU-bound tasks cannot advance grace periods.
* So if the grace period is old enough, make the CPU pay attention.
* Note that the unsynchronized assignments to the per-CPU
* rcu_need_heavy_qs variable are safe. Yes, setting of
* bits can be lost, but they will be set again on the next
* force-quiescent-state pass. So lost bit sets do not result
* in incorrect behavior, merely in a grace period lasting
* a few jiffies longer than it might otherwise. Because
* there are at most four threads involved, and because the
* updates are only once every few jiffies, the probability of
* lossage (and thus of slight grace-period extension) is
* quite low.
*
* Note that if the jiffies_till_sched_qs boot/sysfs parameter
* is set too high, we override with half of the RCU CPU stall
* warning delay.
*/
rnhqp = &per_cpu(rcu_dynticks.rcu_need_heavy_qs, rdp->cpu);
if (!READ_ONCE(*rnhqp) &&
(time_after(jiffies, rdp->rsp->gp_start + jtsq) ||
time_after(jiffies, rdp->rsp->jiffies_resched))) {
WRITE_ONCE(*rnhqp, true);
/* Store rcu_need_heavy_qs before rcu_urgent_qs. */
smp_store_release(ruqp, true);
rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */
}
/*
* If more than halfway to RCU CPU stall-warning time, do
* a resched_cpu() to try to loosen things up a bit.
*/
if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2)
resched_cpu(rdp->cpu);
return 0;
}
static void record_gp_stall_check_time(struct rcu_state *rsp)
{
unsigned long j = jiffies;
unsigned long j1;
rsp->gp_start = j;
smp_wmb(); /* Record start time before stall time. */
j1 = rcu_jiffies_till_stall_check();
WRITE_ONCE(rsp->jiffies_stall, j + j1);
rsp->jiffies_resched = j + j1 / 2;
rsp->n_force_qs_gpstart = READ_ONCE(rsp->n_force_qs);
}
/*
* Convert a ->gp_state value to a character string.
*/
static const char *gp_state_getname(short gs)
{
if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
return "???";
return gp_state_names[gs];
}
/*
* Complain about starvation of grace-period kthread.
*/
static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
{
unsigned long gpa;
unsigned long j;
j = jiffies;
gpa = READ_ONCE(rsp->gp_activity);
if (j - gpa > 2 * HZ) {
pr_err("%s kthread starved for %ld jiffies! g%lu c%lu f%#x %s(%d) ->state=%#lx\n",
rsp->name, j - gpa,
rsp->gpnum, rsp->completed,
rsp->gp_flags,
gp_state_getname(rsp->gp_state), rsp->gp_state,
rsp->gp_kthread ? rsp->gp_kthread->state : ~0);
if (rsp->gp_kthread) {
sched_show_task(rsp->gp_kthread);
wake_up_process(rsp->gp_kthread);
}
}
}
/*
* Dump stacks of all tasks running on stalled CPUs. First try using
* NMIs, but fall back to manual remote stack tracing on architectures
* that don't support NMI-based stack dumps. The NMI-triggered stack
* traces are more accurate because they are printed by the target CPU.
*/
static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
{
int cpu;
unsigned long flags;
struct rcu_node *rnp;
rcu_for_each_leaf_node(rsp, rnp) {
raw_spin_lock_irqsave_rcu_node(rnp, flags);
for_each_leaf_node_possible_cpu(rnp, cpu)
if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
if (!trigger_single_cpu_backtrace(cpu))
dump_cpu_task(cpu);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
}
/*
* If too much time has passed in the current grace period, and if
* so configured, go kick the relevant kthreads.
*/
static void rcu_stall_kick_kthreads(struct rcu_state *rsp)
{
unsigned long j;
if (!rcu_kick_kthreads)
return;
j = READ_ONCE(rsp->jiffies_kick_kthreads);
if (time_after(jiffies, j) && rsp->gp_kthread &&
(rcu_gp_in_progress(rsp) || READ_ONCE(rsp->gp_flags))) {
WARN_ONCE(1, "Kicking %s grace-period kthread\n", rsp->name);
rcu_ftrace_dump(DUMP_ALL);
wake_up_process(rsp->gp_kthread);
WRITE_ONCE(rsp->jiffies_kick_kthreads, j + HZ);
}
}
static inline void panic_on_rcu_stall(void)
{
if (sysctl_panic_on_rcu_stall)
panic("RCU Stall\n");
}
static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
{
int cpu;
long delta;
unsigned long flags;
unsigned long gpa;
unsigned long j;
int ndetected = 0;
struct rcu_node *rnp = rcu_get_root(rsp);
long totqlen = 0;
/* Kick and suppress, if so configured. */
rcu_stall_kick_kthreads(rsp);
if (rcu_cpu_stall_suppress)
return;
/* Only let one CPU complain about others per time interval. */
raw_spin_lock_irqsave_rcu_node(rnp, flags);
delta = jiffies - READ_ONCE(rsp->jiffies_stall);
if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
WRITE_ONCE(rsp->jiffies_stall,
jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
/*
* OK, time to rat on our buddy...
* See Documentation/RCU/stallwarn.txt for info on how to debug
* RCU CPU stall warnings.
*/
pr_err("INFO: %s detected stalls on CPUs/tasks:",
rsp->name);
print_cpu_stall_info_begin();
rcu_for_each_leaf_node(rsp, rnp) {
raw_spin_lock_irqsave_rcu_node(rnp, flags);
ndetected += rcu_print_task_stall(rnp);
if (rnp->qsmask != 0) {
for_each_leaf_node_possible_cpu(rnp, cpu)
if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
print_cpu_stall_info(rsp, cpu);
ndetected++;
}
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
print_cpu_stall_info_end();
for_each_possible_cpu(cpu)
totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
cpu)->cblist);
pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
smp_processor_id(), (long)(jiffies - rsp->gp_start),
(long)rsp->gpnum, (long)rsp->completed, totqlen);
if (ndetected) {
rcu_dump_cpu_stacks(rsp);
/* Complain about tasks blocking the grace period. */
rcu_print_detail_task_stall(rsp);
} else {
if (READ_ONCE(rsp->gpnum) != gpnum ||
READ_ONCE(rsp->completed) == gpnum) {
pr_err("INFO: Stall ended before state dump start\n");
} else {
j = jiffies;
gpa = READ_ONCE(rsp->gp_activity);
pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
rsp->name, j - gpa, j, gpa,
jiffies_till_next_fqs,
rcu_get_root(rsp)->qsmask);
/* In this case, the current CPU might be at fault. */
sched_show_task(current);
}
}
rcu_check_gp_kthread_starvation(rsp);
panic_on_rcu_stall();
force_quiescent_state(rsp); /* Kick them all. */
}
static void print_cpu_stall(struct rcu_state *rsp)
{
int cpu;
unsigned long flags;
struct rcu_node *rnp = rcu_get_root(rsp);
long totqlen = 0;
/* Kick and suppress, if so configured. */
rcu_stall_kick_kthreads(rsp);
if (rcu_cpu_stall_suppress)
return;
/*
* OK, time to rat on ourselves...
* See Documentation/RCU/stallwarn.txt for info on how to debug
* RCU CPU stall warnings.
*/
pr_err("INFO: %s self-detected stall on CPU", rsp->name);
print_cpu_stall_info_begin();
print_cpu_stall_info(rsp, smp_processor_id());
print_cpu_stall_info_end();
for_each_possible_cpu(cpu)
totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
cpu)->cblist);
pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
jiffies - rsp->gp_start,
(long)rsp->gpnum, (long)rsp->completed, totqlen);
rcu_check_gp_kthread_starvation(rsp);
rcu_dump_cpu_stacks(rsp);
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
WRITE_ONCE(rsp->jiffies_stall,
jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
panic_on_rcu_stall();
/*
* Attempt to revive the RCU machinery by forcing a context switch.
*
* A context switch would normally allow the RCU state machine to make
* progress and it could be we're stuck in kernel space without context
* switches for an entirely unreasonable amount of time.
*/
resched_cpu(smp_processor_id());
}
static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
{
unsigned long completed;
unsigned long gpnum;
unsigned long gps;
unsigned long j;
unsigned long js;
struct rcu_node *rnp;
if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
!rcu_gp_in_progress(rsp))
return;
rcu_stall_kick_kthreads(rsp);
j = jiffies;
/*
* Lots of memory barriers to reject false positives.
*
* The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
* then rsp->gp_start, and finally rsp->completed. These values
* are updated in the opposite order with memory barriers (or
* equivalent) during grace-period initialization and cleanup.
* Now, a false positive can occur if we get an new value of
* rsp->gp_start and a old value of rsp->jiffies_stall. But given
* the memory barriers, the only way that this can happen is if one
* grace period ends and another starts between these two fetches.
* Detect this by comparing rsp->completed with the previous fetch
* from rsp->gpnum.
*
* Given this check, comparisons of jiffies, rsp->jiffies_stall,
* and rsp->gp_start suffice to forestall false positives.
*/
gpnum = READ_ONCE(rsp->gpnum);
smp_rmb(); /* Pick up ->gpnum first... */
js = READ_ONCE(rsp->jiffies_stall);
smp_rmb(); /* ...then ->jiffies_stall before the rest... */
gps = READ_ONCE(rsp->gp_start);
smp_rmb(); /* ...and finally ->gp_start before ->completed. */
completed = READ_ONCE(rsp->completed);
if (ULONG_CMP_GE(completed, gpnum) ||
ULONG_CMP_LT(j, js) ||
ULONG_CMP_GE(gps, js))
return; /* No stall or GP completed since entering function. */
rnp = rdp->mynode;
if (rcu_gp_in_progress(rsp) &&
(READ_ONCE(rnp->qsmask) & rdp->grpmask)) {
/* We haven't checked in, so go dump stack. */
print_cpu_stall(rsp);
} else if (rcu_gp_in_progress(rsp) &&
ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
/* They had a few time units to dump stack, so complain. */
print_other_cpu_stall(rsp, gpnum);
}
}
/**
* rcu_cpu_stall_reset - prevent further stall warnings in current grace period
*
* Set the stall-warning timeout way off into the future, thus preventing
* any RCU CPU stall-warning messages from appearing in the current set of
* RCU grace periods.
*
* The caller must disable hard irqs.
*/
void rcu_cpu_stall_reset(void)
{
struct rcu_state *rsp;
for_each_rcu_flavor(rsp)
WRITE_ONCE(rsp->jiffies_stall, jiffies + ULONG_MAX / 2);
}
/*
* Determine the value that ->completed will have at the end of the
* next subsequent grace period. This is used to tag callbacks so that
* a CPU can invoke callbacks in a timely fashion even if that CPU has
* been dyntick-idle for an extended period with callbacks under the
* influence of RCU_FAST_NO_HZ.
*
* The caller must hold rnp->lock with interrupts disabled.
*/
static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
struct rcu_node *rnp)
{
/*
* If RCU is idle, we just wait for the next grace period.
* But we can only be sure that RCU is idle if we are looking
* at the root rcu_node structure -- otherwise, a new grace
* period might have started, but just not yet gotten around
* to initializing the current non-root rcu_node structure.
*/
if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed)
return rnp->completed + 1;
/*
* Otherwise, wait for a possible partial grace period and
* then the subsequent full grace period.
*/
return rnp->completed + 2;
}
/*
* Trace-event helper function for rcu_start_future_gp() and
* rcu_nocb_wait_gp().
*/
static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
unsigned long c, const char *s)
{
trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
rnp->completed, c, rnp->level,
rnp->grplo, rnp->grphi, s);
}
/*
* Start some future grace period, as needed to handle newly arrived
* callbacks. The required future grace periods are recorded in each
* rcu_node structure's ->need_future_gp field. Returns true if there
* is reason to awaken the grace-period kthread.
*
* The caller must hold the specified rcu_node structure's ->lock.
*/
static bool __maybe_unused
rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
unsigned long *c_out)
{
unsigned long c;
bool ret = false;
struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
/*
* Pick up grace-period number for new callbacks. If this
* grace period is already marked as needed, return to the caller.
*/
c = rcu_cbs_completed(rdp->rsp, rnp);
trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
if (rnp->need_future_gp[c & 0x1]) {
trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
goto out;
}
/*
* If either this rcu_node structure or the root rcu_node structure
* believe that a grace period is in progress, then we must wait
* for the one following, which is in "c". Because our request
* will be noticed at the end of the current grace period, we don't
* need to explicitly start one. We only do the lockless check
* of rnp_root's fields if the current rcu_node structure thinks
* there is no grace period in flight, and because we hold rnp->lock,
* the only possible change is when rnp_root's two fields are
* equal, in which case rnp_root->gpnum might be concurrently
* incremented. But that is OK, as it will just result in our
* doing some extra useless work.
*/
if (rnp->gpnum != rnp->completed ||
READ_ONCE(rnp_root->gpnum) != READ_ONCE(rnp_root->completed)) {
rnp->need_future_gp[c & 0x1]++;
trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
goto out;
}
/*
* There might be no grace period in progress. If we don't already
* hold it, acquire the root rcu_node structure's lock in order to
* start one (if needed).
*/
if (rnp != rnp_root)
raw_spin_lock_rcu_node(rnp_root);
/*
* Get a new grace-period number. If there really is no grace
* period in progress, it will be smaller than the one we obtained
* earlier. Adjust callbacks as needed.
*/
c = rcu_cbs_completed(rdp->rsp, rnp_root);
if (!rcu_is_nocb_cpu(rdp->cpu))
(void)rcu_segcblist_accelerate(&rdp->cblist, c);
/*
* If the needed for the required grace period is already
* recorded, trace and leave.
*/
if (rnp_root->need_future_gp[c & 0x1]) {
trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
goto unlock_out;
}
/* Record the need for the future grace period. */
rnp_root->need_future_gp[c & 0x1]++;
/* If a grace period is not already in progress, start one. */
if (rnp_root->gpnum != rnp_root->completed) {
trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
} else {
trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
ret = rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
}
unlock_out:
if (rnp != rnp_root)
raw_spin_unlock_rcu_node(rnp_root);
out:
if (c_out != NULL)
*c_out = c;
return ret;
}
/*
* Clean up any old requests for the just-ended grace period. Also return
* whether any additional grace periods have been requested. Also invoke
* rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads
* waiting for this grace period to complete.
*/
static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
{
int c = rnp->completed;
int needmore;
struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
rnp->need_future_gp[c & 0x1] = 0;
needmore = rnp->need_future_gp[(c + 1) & 0x1];
trace_rcu_future_gp(rnp, rdp, c,
needmore ? TPS("CleanupMore") : TPS("Cleanup"));
return needmore;
}
/*
* Awaken the grace-period kthread for the specified flavor of RCU.
* Don't do a self-awaken, and don't bother awakening when there is
* nothing for the grace-period kthread to do (as in several CPUs
* raced to awaken, and we lost), and finally don't try to awaken
* a kthread that has not yet been created.
*/
static void rcu_gp_kthread_wake(struct rcu_state *rsp)
{
if (current == rsp->gp_kthread ||
!READ_ONCE(rsp->gp_flags) ||
!rsp->gp_kthread)
return;
swake_up(&rsp->gp_wq);
}
/*
* If there is room, assign a ->completed number to any callbacks on
* this CPU that have not already been assigned. Also accelerate any
* callbacks that were previously assigned a ->completed number that has
* since proven to be too conservative, which can happen if callbacks get
* assigned a ->completed number while RCU is idle, but with reference to
* a non-root rcu_node structure. This function is idempotent, so it does
* not hurt to call it repeatedly. Returns an flag saying that we should
* awaken the RCU grace-period kthread.
*
* The caller must hold rnp->lock with interrupts disabled.
*/
static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
struct rcu_data *rdp)
{
bool ret = false;
/* If no pending (not yet ready to invoke) callbacks, nothing to do. */
if (!rcu_segcblist_pend_cbs(&rdp->cblist))
return false;
/*
* Callbacks are often registered with incomplete grace-period
* information. Something about the fact that getting exact
* information requires acquiring a global lock... RCU therefore
* makes a conservative estimate of the grace period number at which
* a given callback will become ready to invoke. The following
* code checks this estimate and improves it when possible, thus
* accelerating callback invocation to an earlier grace-period
* number.
*/
if (rcu_segcblist_accelerate(&rdp->cblist, rcu_cbs_completed(rsp, rnp)))
ret = rcu_start_future_gp(rnp, rdp, NULL);
/* Trace depending on how much we were able to accelerate. */
if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
else
trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
return ret;
}
/*
* Move any callbacks whose grace period has completed to the
* RCU_DONE_TAIL sublist, then compact the remaining sublists and
* assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
* sublist. This function is idempotent, so it does not hurt to
* invoke it repeatedly. As long as it is not invoked -too- often...
* Returns true if the RCU grace-period kthread needs to be awakened.
*
* The caller must hold rnp->lock with interrupts disabled.
*/
static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
struct rcu_data *rdp)
{
/* If no pending (not yet ready to invoke) callbacks, nothing to do. */
if (!rcu_segcblist_pend_cbs(&rdp->cblist))
return false;
/*
* Find all callbacks whose ->completed numbers indicate that they
* are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
*/
rcu_segcblist_advance(&rdp->cblist, rnp->completed);
/* Classify any remaining callbacks. */
return rcu_accelerate_cbs(rsp, rnp, rdp);
}
/*
* Update CPU-local rcu_data state to record the beginnings and ends of
* grace periods. The caller must hold the ->lock of the leaf rcu_node
* structure corresponding to the current CPU, and must have irqs disabled.
* Returns true if the grace-period kthread needs to be awakened.
*/
static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
struct rcu_data *rdp)
{
bool ret;
bool need_gp;
/* Handle the ends of any preceding grace periods first. */
if (rdp->completed == rnp->completed &&
!unlikely(READ_ONCE(rdp->gpwrap))) {
/* No grace period end, so just accelerate recent callbacks. */
ret = rcu_accelerate_cbs(rsp, rnp, rdp);
} else {
/* Advance callbacks. */
ret = rcu_advance_cbs(rsp, rnp, rdp);
/* Remember that we saw this grace-period completion. */
rdp->completed = rnp->completed;
trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
}
if (rdp->gpnum != rnp->gpnum || unlikely(READ_ONCE(rdp->gpwrap))) {
/*
* If the current grace period is waiting for this CPU,
* set up to detect a quiescent state, otherwise don't
* go looking for one.
*/
rdp->gpnum = rnp->gpnum;
trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
need_gp = !!(rnp->qsmask & rdp->grpmask);
rdp->cpu_no_qs.b.norm = need_gp;
rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr);
rdp->core_needs_qs = need_gp;
zero_cpu_stall_ticks(rdp);
WRITE_ONCE(rdp->gpwrap, false);
}
return ret;
}
static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
{
unsigned long flags;
bool needwake;
struct rcu_node *rnp;
local_irq_save(flags);
rnp = rdp->mynode;
if ((rdp->gpnum == READ_ONCE(rnp->gpnum) &&
rdp->completed == READ_ONCE(rnp->completed) &&
!unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
!raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
local_irq_restore(flags);
return;
}
needwake = __note_gp_changes(rsp, rnp, rdp);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
if (needwake)
rcu_gp_kthread_wake(rsp);
}
static void rcu_gp_slow(struct rcu_state *rsp, int delay)
{
if (delay > 0 &&
!(rsp->gpnum % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
schedule_timeout_uninterruptible(delay);
}
/*
* Initialize a new grace period. Return false if no grace period required.
*/
static bool rcu_gp_init(struct rcu_state *rsp)
{
unsigned long oldmask;
struct rcu_data *rdp;
struct rcu_node *rnp = rcu_get_root(rsp);
WRITE_ONCE(rsp->gp_activity, jiffies);
raw_spin_lock_irq_rcu_node(rnp);
if (!READ_ONCE(rsp->gp_flags)) {
/* Spurious wakeup, tell caller to go back to sleep. */
raw_spin_unlock_irq_rcu_node(rnp);
return false;
}
WRITE_ONCE(rsp->gp_flags, 0); /* Clear all flags: New grace period. */
if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
/*
* Grace period already in progress, don't start another.
* Not supposed to be able to happen.
*/
raw_spin_unlock_irq_rcu_node(rnp);
return false;
}
/* Advance to a new grace period and initialize state. */
record_gp_stall_check_time(rsp);
/* Record GP times before starting GP, hence smp_store_release(). */
smp_store_release(&rsp->gpnum, rsp->gpnum + 1);
trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
raw_spin_unlock_irq_rcu_node(rnp);
/*
* Apply per-leaf buffered online and offline operations to the
* rcu_node tree. Note that this new grace period need not wait
* for subsequent online CPUs, and that quiescent-state forcing
* will handle subsequent offline CPUs.
*/
rcu_for_each_leaf_node(rsp, rnp) {
rcu_gp_slow(rsp, gp_preinit_delay);
raw_spin_lock_irq_rcu_node(rnp);
if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
!rnp->wait_blkd_tasks) {
/* Nothing to do on this leaf rcu_node structure. */
raw_spin_unlock_irq_rcu_node(rnp);
continue;
}
/* Record old state, apply changes to ->qsmaskinit field. */
oldmask = rnp->qsmaskinit;
rnp->qsmaskinit = rnp->qsmaskinitnext;
/* If zero-ness of ->qsmaskinit changed, propagate up tree. */
if (!oldmask != !rnp->qsmaskinit) {
if (!oldmask) /* First online CPU for this rcu_node. */
rcu_init_new_rnp(rnp);
else if (rcu_preempt_has_tasks(rnp)) /* blocked tasks */
rnp->wait_blkd_tasks = true;
else /* Last offline CPU and can propagate. */
rcu_cleanup_dead_rnp(rnp);
}
/*
* If all waited-on tasks from prior grace period are
* done, and if all this rcu_node structure's CPUs are
* still offline, propagate up the rcu_node tree and
* clear ->wait_blkd_tasks. Otherwise, if one of this
* rcu_node structure's CPUs has since come back online,
* simply clear ->wait_blkd_tasks (but rcu_cleanup_dead_rnp()
* checks for this, so just call it unconditionally).
*/
if (rnp->wait_blkd_tasks &&
(!rcu_preempt_has_tasks(rnp) ||
rnp->qsmaskinit)) {
rnp->wait_blkd_tasks = false;
rcu_cleanup_dead_rnp(rnp);
}
raw_spin_unlock_irq_rcu_node(rnp);
}
/*
* Set the quiescent-state-needed bits in all the rcu_node
* structures for all currently online CPUs in breadth-first order,
* starting from the root rcu_node structure, relying on the layout
* of the tree within the rsp->node[] array. Note that other CPUs
* will access only the leaves of the hierarchy, thus seeing that no
* grace period is in progress, at least until the corresponding
* leaf node has been initialized.
*
* The grace period cannot complete until the initialization
* process finishes, because this kthread handles both.
*/
rcu_for_each_node_breadth_first(rsp, rnp) {
rcu_gp_slow(rsp, gp_init_delay);
raw_spin_lock_irq_rcu_node(rnp);
rdp = this_cpu_ptr(rsp->rda);
rcu_preempt_check_blocked_tasks(rnp);
rnp->qsmask = rnp->qsmaskinit;
WRITE_ONCE(rnp->gpnum, rsp->gpnum);
if (WARN_ON_ONCE(rnp->completed != rsp->completed))
WRITE_ONCE(rnp->completed, rsp->completed);
if (rnp == rdp->mynode)
(void)__note_gp_changes(rsp, rnp, rdp);
rcu_preempt_boost_start_gp(rnp);
trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
rnp->level, rnp->grplo,
rnp->grphi, rnp->qsmask);
raw_spin_unlock_irq_rcu_node(rnp);
cond_resched_rcu_qs();
WRITE_ONCE(rsp->gp_activity, jiffies);
}
return true;
}
/*
* Helper function for wait_event_interruptible_timeout() wakeup
* at force-quiescent-state time.
*/
static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
{
struct rcu_node *rnp = rcu_get_root(rsp);
/* Someone like call_rcu() requested a force-quiescent-state scan. */
*gfp = READ_ONCE(rsp->gp_flags);
if (*gfp & RCU_GP_FLAG_FQS)
return true;
/* The current grace period has completed. */
if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
return true;
return false;
}
/*
* Do one round of quiescent-state forcing.
*/
static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time)
{
bool isidle = false;
unsigned long maxj;
struct rcu_node *rnp = rcu_get_root(rsp);
WRITE_ONCE(rsp->gp_activity, jiffies);
rsp->n_force_qs++;
if (first_time) {
/* Collect dyntick-idle snapshots. */
if (is_sysidle_rcu_state(rsp)) {
isidle = true;
maxj = jiffies - ULONG_MAX / 4;
}
force_qs_rnp(rsp, dyntick_save_progress_counter,
&isidle, &maxj);
rcu_sysidle_report_gp(rsp, isidle, maxj);
} else {
/* Handle dyntick-idle and offline CPUs. */
isidle = true;
force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj);
}
/* Clear flag to prevent immediate re-entry. */
if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
raw_spin_lock_irq_rcu_node(rnp);
WRITE_ONCE(rsp->gp_flags,
READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS);
raw_spin_unlock_irq_rcu_node(rnp);
}
}
/*
* Clean up after the old grace period.
*/
static void rcu_gp_cleanup(struct rcu_state *rsp)
{
unsigned long gp_duration;
bool needgp = false;
int nocb = 0;
struct rcu_data *rdp;
struct rcu_node *rnp = rcu_get_root(rsp);
struct swait_queue_head *sq;
WRITE_ONCE(rsp->gp_activity, jiffies);
raw_spin_lock_irq_rcu_node(rnp);
gp_duration = jiffies - rsp->gp_start;
if (gp_duration > rsp->gp_max)
rsp->gp_max = gp_duration;
/*
* We know the grace period is complete, but to everyone else
* it appears to still be ongoing. But it is also the case
* that to everyone else it looks like there is nothing that
* they can do to advance the grace period. It is therefore
* safe for us to drop the lock in order to mark the grace
* period as completed in all of the rcu_node structures.
*/
raw_spin_unlock_irq_rcu_node(rnp);
/*
* Propagate new ->completed value to rcu_node structures so
* that other CPUs don't have to wait until the start of the next
* grace period to process their callbacks. This also avoids
* some nasty RCU grace-period initialization races by forcing
* the end of the current grace period to be completely recorded in
* all of the rcu_node structures before the beginning of the next
* grace period is recorded in any of the rcu_node structures.
*/
rcu_for_each_node_breadth_first(rsp, rnp) {
raw_spin_lock_irq_rcu_node(rnp);
WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
WARN_ON_ONCE(rnp->qsmask);
WRITE_ONCE(rnp->completed, rsp->gpnum);
rdp = this_cpu_ptr(rsp->rda);
if (rnp == rdp->mynode)
needgp = __note_gp_changes(rsp, rnp, rdp) || needgp;
/* smp_mb() provided by prior unlock-lock pair. */
nocb += rcu_future_gp_cleanup(rsp, rnp);
sq = rcu_nocb_gp_get(rnp);
raw_spin_unlock_irq_rcu_node(rnp);
rcu_nocb_gp_cleanup(sq);
cond_resched_rcu_qs();
WRITE_ONCE(rsp->gp_activity, jiffies);
rcu_gp_slow(rsp, gp_cleanup_delay);
}
rnp = rcu_get_root(rsp);
raw_spin_lock_irq_rcu_node(rnp); /* Order GP before ->completed update. */
rcu_nocb_gp_set(rnp, nocb);
/* Declare grace period done. */
WRITE_ONCE(rsp->completed, rsp->gpnum);
trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
rsp->gp_state = RCU_GP_IDLE;
rdp = this_cpu_ptr(rsp->rda);
/* Advance CBs to reduce false positives below. */
needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
if (needgp || cpu_needs_another_gp(rsp, rdp)) {
WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("newreq"));
}
raw_spin_unlock_irq_rcu_node(rnp);
}
/*
* Body of kthread that handles grace periods.
*/
static int __noreturn rcu_gp_kthread(void *arg)
{
bool first_gp_fqs;
int gf;
unsigned long j;
int ret;
struct rcu_state *rsp = arg;
struct rcu_node *rnp = rcu_get_root(rsp);
rcu_bind_gp_kthread();
for (;;) {
/* Handle grace-period start. */
for (;;) {
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("reqwait"));
rsp->gp_state = RCU_GP_WAIT_GPS;
swait_event_interruptible(rsp->gp_wq,
READ_ONCE(rsp->gp_flags) &
RCU_GP_FLAG_INIT);
rsp->gp_state = RCU_GP_DONE_GPS;
/* Locking provides needed memory barrier. */
if (rcu_gp_init(rsp))
break;
cond_resched_rcu_qs();
WRITE_ONCE(rsp->gp_activity, jiffies);
WARN_ON(signal_pending(current));
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("reqwaitsig"));
}
/* Handle quiescent-state forcing. */
first_gp_fqs = true;
j = jiffies_till_first_fqs;
if (j > HZ) {
j = HZ;
jiffies_till_first_fqs = HZ;
}
ret = 0;
for (;;) {
if (!ret) {
rsp->jiffies_force_qs = jiffies + j;
WRITE_ONCE(rsp->jiffies_kick_kthreads,
jiffies + 3 * j);
}
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("fqswait"));
rsp->gp_state = RCU_GP_WAIT_FQS;
ret = swait_event_interruptible_timeout(rsp->gp_wq,
rcu_gp_fqs_check_wake(rsp, &gf), j);
rsp->gp_state = RCU_GP_DOING_FQS;
/* Locking provides needed memory barriers. */
/* If grace period done, leave loop. */
if (!READ_ONCE(rnp->qsmask) &&
!rcu_preempt_blocked_readers_cgp(rnp))
break;
/* If time for quiescent-state forcing, do it. */
if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
(gf & RCU_GP_FLAG_FQS)) {
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("fqsstart"));
rcu_gp_fqs(rsp, first_gp_fqs);
first_gp_fqs = false;
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("fqsend"));
cond_resched_rcu_qs();
WRITE_ONCE(rsp->gp_activity, jiffies);
ret = 0; /* Force full wait till next FQS. */
j = jiffies_till_next_fqs;
if (j > HZ) {
j = HZ;
jiffies_till_next_fqs = HZ;
} else if (j < 1) {
j = 1;
jiffies_till_next_fqs = 1;
}
} else {
/* Deal with stray signal. */
cond_resched_rcu_qs();
WRITE_ONCE(rsp->gp_activity, jiffies);
WARN_ON(signal_pending(current));
trace_rcu_grace_period(rsp->name,
READ_ONCE(rsp->gpnum),
TPS("fqswaitsig"));
ret = 1; /* Keep old FQS timing. */
j = jiffies;
if (time_after(jiffies, rsp->jiffies_force_qs))
j = 1;
else
j = rsp->jiffies_force_qs - j;
}
}
/* Handle grace-period end. */
rsp->gp_state = RCU_GP_CLEANUP;
rcu_gp_cleanup(rsp);
rsp->gp_state = RCU_GP_CLEANED;
}
}
/*
* Start a new RCU grace period if warranted, re-initializing the hierarchy
* in preparation for detecting the next grace period. The caller must hold
* the root node's ->lock and hard irqs must be disabled.
*
* Note that it is legal for a dying CPU (which is marked as offline) to
* invoke this function. This can happen when the dying CPU reports its
* quiescent state.
*
* Returns true if the grace-period kthread must be awakened.
*/
static bool
rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
struct rcu_data *rdp)
{
if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
/*
* Either we have not yet spawned the grace-period
* task, this CPU does not need another grace period,
* or a grace period is already in progress.
* Either way, don't start a new grace period.
*/
return false;
}
WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum),
TPS("newreq"));
/*
* We can't do wakeups while holding the rnp->lock, as that
* could cause possible deadlocks with the rq->lock. Defer
* the wakeup to our caller.
*/
return true;
}
/*
* Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
* callbacks. Note that rcu_start_gp_advanced() cannot do this because it
* is invoked indirectly from rcu_advance_cbs(), which would result in
* endless recursion -- or would do so if it wasn't for the self-deadlock
* that is encountered beforehand.
*
* Returns true if the grace-period kthread needs to be awakened.
*/
static bool rcu_start_gp(struct rcu_state *rsp)
{
struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
struct rcu_node *rnp = rcu_get_root(rsp);
bool ret = false;
/*
* If there is no grace period in progress right now, any
* callbacks we have up to this point will be satisfied by the
* next grace period. Also, advancing the callbacks reduces the
* probability of false positives from cpu_needs_another_gp()
* resulting in pointless grace periods. So, advance callbacks
* then start the grace period!
*/
ret = rcu_advance_cbs(rsp, rnp, rdp) || ret;
ret = rcu_start_gp_advanced(rsp, rnp, rdp) || ret;
return ret;
}
/*
* Report a full set of quiescent states to the specified rcu_state data
* structure. Invoke rcu_gp_kthread_wake() to awaken the grace-period
* kthread if another grace period is required. Whether we wake
* the grace-period kthread or it awakens itself for the next round
* of quiescent-state forcing, that kthread will clean up after the
* just-completed grace period. Note that the caller must hold rnp->lock,
* which is released before return.
*/
static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
__releases(rcu_get_root(rsp)->lock)
{
WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags);
rcu_gp_kthread_wake(rsp);
}
/*
* Similar to rcu_report_qs_rdp(), for which it is a helper function.
* Allows quiescent states for a group of CPUs to be reported at one go
* to the specified rcu_node structure, though all the CPUs in the group
* must be represented by the same rcu_node structure (which need not be a
* leaf rcu_node structure, though it often will be). The gps parameter
* is the grace-period snapshot, which means that the quiescent states
* are valid only if rnp->gpnum is equal to gps. That structure's lock
* must be held upon entry, and it is released before return.
*/
static void
rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
struct rcu_node *rnp, unsigned long gps, unsigned long flags)
__releases(rnp->lock)
{
unsigned long oldmask = 0;
struct rcu_node *rnp_c;
/* Walk up the rcu_node hierarchy. */
for (;;) {
if (!(rnp->qsmask & mask) || rnp->gpnum != gps) {
/*
* Our bit has already been cleared, or the
* relevant grace period is already over, so done.
*/
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
rnp->qsmask &= ~mask;
trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
mask, rnp->qsmask, rnp->level,
rnp->grplo, rnp->grphi,
!!rnp->gp_tasks);
if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
/* Other bits still set at this level, so done. */
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
mask = rnp->grpmask;
if (rnp->parent == NULL) {
/* No more levels. Exit loop holding root lock. */
break;
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
rnp_c = rnp;
rnp = rnp->parent;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
oldmask = rnp_c->qsmask;
}
/*
* Get here if we are the last CPU to pass through a quiescent
* state for this grace period. Invoke rcu_report_qs_rsp()
* to clean up and start the next grace period if one is needed.
*/
rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
}
/*
* Record a quiescent state for all tasks that were previously queued
* on the specified rcu_node structure and that were blocking the current
* RCU grace period. The caller must hold the specified rnp->lock with
* irqs disabled, and this lock is released upon return, but irqs remain
* disabled.
*/
static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp,
struct rcu_node *rnp, unsigned long flags)
__releases(rnp->lock)
{
unsigned long gps;
unsigned long mask;
struct rcu_node *rnp_p;
if (rcu_state_p == &rcu_sched_state || rsp != rcu_state_p ||
rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return; /* Still need more quiescent states! */
}
rnp_p = rnp->parent;
if (rnp_p == NULL) {
/*
* Only one rcu_node structure in the tree, so don't
* try to report up to its nonexistent parent!
*/
rcu_report_qs_rsp(rsp, flags);
return;
}
/* Report up the rest of the hierarchy, tracking current ->gpnum. */
gps = rnp->gpnum;
mask = rnp->grpmask;
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */
rcu_report_qs_rnp(mask, rsp, rnp_p, gps, flags);
}
/*
* Record a quiescent state for the specified CPU to that CPU's rcu_data
* structure. This must be called from the specified CPU.
*/
static void
rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
{
unsigned long flags;
unsigned long mask;
bool needwake;
struct rcu_node *rnp;
rnp = rdp->mynode;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (rdp->cpu_no_qs.b.norm || rdp->gpnum != rnp->gpnum ||
rnp->completed == rnp->gpnum || rdp->gpwrap) {
/*
* The grace period in which this quiescent state was
* recorded has ended, so don't report it upwards.
* We will instead need a new quiescent state that lies
* within the current grace period.
*/
rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
mask = rdp->grpmask;
if ((rnp->qsmask & mask) == 0) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
} else {
rdp->core_needs_qs = false;
/*
* This GP can't end until cpu checks in, so all of our
* callbacks can be processed during the next GP.
*/
needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
/* ^^^ Released rnp->lock */
if (needwake)
rcu_gp_kthread_wake(rsp);
}
}
/*
* Check to see if there is a new grace period of which this CPU
* is not yet aware, and if so, set up local rcu_data state for it.
* Otherwise, see if this CPU has just passed through its first
* quiescent state for this grace period, and record that fact if so.
*/
static void
rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
{
/* Check for grace-period ends and beginnings. */
note_gp_changes(rsp, rdp);
/*
* Does this CPU still need to do its part for current grace period?
* If no, return and let the other CPUs do their part as well.
*/
if (!rdp->core_needs_qs)
return;
/*
* Was there a quiescent state since the beginning of the grace
* period? If no, then exit and wait for the next call.
*/
if (rdp->cpu_no_qs.b.norm)
return;
/*
* Tell RCU we are done (but rcu_report_qs_rdp() will be the
* judge of that).
*/
rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
}
/*
* Send the specified CPU's RCU callbacks to the orphanage. The
* specified CPU must be offline, and the caller must hold the
* ->orphan_lock.
*/
static void
rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
struct rcu_node *rnp, struct rcu_data *rdp)
{
/* No-CBs CPUs do not have orphanable callbacks. */
if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || rcu_is_nocb_cpu(rdp->cpu))
return;
/*
* Orphan the callbacks. First adjust the counts. This is safe
* because _rcu_barrier() excludes CPU-hotplug operations, so it
* cannot be running now. Thus no memory barrier is required.
*/
rdp->n_cbs_orphaned += rcu_segcblist_n_cbs(&rdp->cblist);
rcu_segcblist_extract_count(&rdp->cblist, &rsp->orphan_done);
/*
* Next, move those callbacks still needing a grace period to
* the orphanage, where some other CPU will pick them up.
* Some of the callbacks might have gone partway through a grace
* period, but that is too bad. They get to start over because we
* cannot assume that grace periods are synchronized across CPUs.
*/
rcu_segcblist_extract_pend_cbs(&rdp->cblist, &rsp->orphan_pend);
/*
* Then move the ready-to-invoke callbacks to the orphanage,
* where some other CPU will pick them up. These will not be
* required to pass though another grace period: They are done.
*/
rcu_segcblist_extract_done_cbs(&rdp->cblist, &rsp->orphan_done);
/* Finally, disallow further callbacks on this CPU. */
rcu_segcblist_disable(&rdp->cblist);
}
/*
* Adopt the RCU callbacks from the specified rcu_state structure's
* orphanage. The caller must hold the ->orphan_lock.
*/
static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
{
struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
/* No-CBs CPUs are handled specially. */
if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
rcu_nocb_adopt_orphan_cbs(rsp, rdp, flags))
return;
/* Do the accounting first. */
rdp->n_cbs_adopted += rcu_cblist_n_cbs(&rsp->orphan_done);
if (rcu_cblist_n_lazy_cbs(&rsp->orphan_done) !=
rcu_cblist_n_cbs(&rsp->orphan_done))
rcu_idle_count_callbacks_posted();
rcu_segcblist_insert_count(&rdp->cblist, &rsp->orphan_done);
/*
* We do not need a memory barrier here because the only way we
* can get here if there is an rcu_barrier() in flight is if
* we are the task doing the rcu_barrier().
*/
/* First adopt the ready-to-invoke callbacks, then the done ones. */
rcu_segcblist_insert_done_cbs(&rdp->cblist, &rsp->orphan_done);
WARN_ON_ONCE(!rcu_cblist_empty(&rsp->orphan_done));
rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rsp->orphan_pend);
WARN_ON_ONCE(!rcu_cblist_empty(&rsp->orphan_pend));
WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) !=
!rcu_segcblist_n_cbs(&rdp->cblist));
}
/*
* Trace the fact that this CPU is going offline.
*/
static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
{
RCU_TRACE(unsigned long mask;)
RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda);)
RCU_TRACE(struct rcu_node *rnp = rdp->mynode;)
if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
return;
RCU_TRACE(mask = rdp->grpmask;)
trace_rcu_grace_period(rsp->name,
rnp->gpnum + 1 - !!(rnp->qsmask & mask),
TPS("cpuofl"));
}
/*
* All CPUs for the specified rcu_node structure have gone offline,
* and all tasks that were preempted within an RCU read-side critical
* section while running on one of those CPUs have since exited their RCU
* read-side critical section. Some other CPU is reporting this fact with
* the specified rcu_node structure's ->lock held and interrupts disabled.
* This function therefore goes up the tree of rcu_node structures,
* clearing the corresponding bits in the ->qsmaskinit fields. Note that
* the leaf rcu_node structure's ->qsmaskinit field has already been
* updated
*
* This function does check that the specified rcu_node structure has
* all CPUs offline and no blocked tasks, so it is OK to invoke it
* prematurely. That said, invoking it after the fact will cost you
* a needless lock acquisition. So once it has done its work, don't
* invoke it again.
*/
static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
{
long mask;
struct rcu_node *rnp = rnp_leaf;
if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
rnp->qsmaskinit || rcu_preempt_has_tasks(rnp))
return;
for (;;) {
mask = rnp->grpmask;
rnp = rnp->parent;
if (!rnp)
break;
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
rnp->qsmaskinit &= ~mask;
rnp->qsmask &= ~mask;
if (rnp->qsmaskinit) {
raw_spin_unlock_rcu_node(rnp);
/* irqs remain disabled. */
return;
}
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
}
}
/*
* The CPU has been completely removed, and some other CPU is reporting
* this fact from process context. Do the remainder of the cleanup,
* including orphaning the outgoing CPU's RCU callbacks, and also
* adopting them. There can only be one CPU hotplug operation at a time,
* so no other CPU can be attempting to update rcu_cpu_kthread_task.
*/
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
{
unsigned long flags;
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
return;
/* Adjust any no-longer-needed kthreads. */
rcu_boost_kthread_setaffinity(rnp, -1);
/* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
rcu_adopt_orphan_cbs(rsp, flags);
raw_spin_unlock_irqrestore(&rsp->orphan_lock, flags);
WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
!rcu_segcblist_empty(&rdp->cblist),
"rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
cpu, rcu_segcblist_n_cbs(&rdp->cblist),
rcu_segcblist_first_cb(&rdp->cblist));
}
/*
* Invoke any RCU callbacks that have made it to the end of their grace
* period. Thottle as specified by rdp->blimit.
*/
static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
{
unsigned long flags;
struct rcu_head *rhp;
struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
long bl, count;
/* If no callbacks are ready, just return. */
if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
trace_rcu_batch_start(rsp->name,
rcu_segcblist_n_lazy_cbs(&rdp->cblist),
rcu_segcblist_n_cbs(&rdp->cblist), 0);
trace_rcu_batch_end(rsp->name, 0,
!rcu_segcblist_empty(&rdp->cblist),
need_resched(), is_idle_task(current),
rcu_is_callbacks_kthread());
return;
}
/*
* Extract the list of ready callbacks, disabling to prevent
* races with call_rcu() from interrupt handlers. Leave the
* callback counts, as rcu_barrier() needs to be conservative.
*/
local_irq_save(flags);
WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
bl = rdp->blimit;
trace_rcu_batch_start(rsp->name, rcu_segcblist_n_lazy_cbs(&rdp->cblist),
rcu_segcblist_n_cbs(&rdp->cblist), bl);
rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
local_irq_restore(flags);
/* Invoke callbacks. */
rhp = rcu_cblist_dequeue(&rcl);
for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
debug_rcu_head_unqueue(rhp);
if (__rcu_reclaim(rsp->name, rhp))
rcu_cblist_dequeued_lazy(&rcl);
/*
* Stop only if limit reached and CPU has something to do.
* Note: The rcl structure counts down from zero.
*/
if (-rcu_cblist_n_cbs(&rcl) >= bl &&
(need_resched() ||
(!is_idle_task(current) && !rcu_is_callbacks_kthread())))
break;
}
local_irq_save(flags);
count = -rcu_cblist_n_cbs(&rcl);
trace_rcu_batch_end(rsp->name, count, !rcu_cblist_empty(&rcl),
need_resched(), is_idle_task(current),
rcu_is_callbacks_kthread());
/* Update counts and requeue any remaining callbacks. */
rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
smp_mb(); /* List handling before counting for rcu_barrier(). */
rdp->n_cbs_invoked += count;
rcu_segcblist_insert_count(&rdp->cblist, &rcl);
/* Reinstate batch limit if we have worked down the excess. */
count = rcu_segcblist_n_cbs(&rdp->cblist);
if (rdp->blimit == LONG_MAX && count <= qlowmark)
rdp->blimit = blimit;
/* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
if (count == 0 && rdp->qlen_last_fqs_check != 0) {
rdp->qlen_last_fqs_check = 0;
rdp->n_force_qs_snap = rsp->n_force_qs;
} else if (count < rdp->qlen_last_fqs_check - qhimark)
rdp->qlen_last_fqs_check = count;
WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) != (count == 0));
local_irq_restore(flags);
/* Re-invoke RCU core processing if there are callbacks remaining. */
if (rcu_segcblist_ready_cbs(&rdp->cblist))
invoke_rcu_core();
}
/*
* Check to see if this CPU is in a non-context-switch quiescent state
* (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
* Also schedule RCU core processing.
*
* This function must be called from hardirq context. It is normally
* invoked from the scheduling-clock interrupt.
*/
void rcu_check_callbacks(int user)
{
trace_rcu_utilization(TPS("Start scheduler-tick"));
increment_cpu_stall_ticks();
if (user || rcu_is_cpu_rrupt_from_idle()) {
/*
* Get here if this CPU took its interrupt from user
* mode or from the idle loop, and if this is not a
* nested interrupt. In this case, the CPU is in
* a quiescent state, so note it.
*
* No memory barrier is required here because both
* rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
* variables that other CPUs neither access nor modify,
* at least not while the corresponding CPU is online.
*/
rcu_sched_qs();
rcu_bh_qs();
} else if (!in_softirq()) {
/*
* Get here if this CPU did not take its interrupt from
* softirq, in other words, if it is not interrupting
* a rcu_bh read-side critical section. This is an _bh
* critical section, so note it.
*/
rcu_bh_qs();
}
rcu_preempt_check_callbacks();
if (rcu_pending())
invoke_rcu_core();
if (user)
rcu_note_voluntary_context_switch(current);
trace_rcu_utilization(TPS("End scheduler-tick"));
}
/*
* Scan the leaf rcu_node structures, processing dyntick state for any that
* have not yet encountered a quiescent state, using the function specified.
* Also initiate boosting for any threads blocked on the root rcu_node.
*
* The caller must have suppressed start of new grace periods.
*/
static void force_qs_rnp(struct rcu_state *rsp,
int (*f)(struct rcu_data *rsp, bool *isidle,
unsigned long *maxj),
bool *isidle, unsigned long *maxj)
{
int cpu;
unsigned long flags;
unsigned long mask;
struct rcu_node *rnp;
rcu_for_each_leaf_node(rsp, rnp) {
cond_resched_rcu_qs();
mask = 0;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (rnp->qsmask == 0) {
if (rcu_state_p == &rcu_sched_state ||
rsp != rcu_state_p ||
rcu_preempt_blocked_readers_cgp(rnp)) {
/*
* No point in scanning bits because they
* are all zero. But we might need to
* priority-boost blocked readers.
*/
rcu_initiate_boost(rnp, flags);
/* rcu_initiate_boost() releases rnp->lock */
continue;
}
if (rnp->parent &&
(rnp->parent->qsmask & rnp->grpmask)) {
/*
* Race between grace-period
* initialization and task exiting RCU
* read-side critical section: Report.
*/
rcu_report_unblock_qs_rnp(rsp, rnp, flags);
/* rcu_report_unblock_qs_rnp() rlses ->lock */
continue;
}
}
for_each_leaf_node_possible_cpu(rnp, cpu) {
unsigned long bit = leaf_node_cpu_bit(rnp, cpu);
if ((rnp->qsmask & bit) != 0) {
if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
mask |= bit;
}
}
if (mask != 0) {
/* Idle/offline CPUs, report (releases rnp->lock. */
rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
} else {
/* Nothing to do here, so just drop the lock. */
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
}
}
/*
* Force quiescent states on reluctant CPUs, and also detect which
* CPUs are in dyntick-idle mode.
*/
static void force_quiescent_state(struct rcu_state *rsp)
{
unsigned long flags;
bool ret;
struct rcu_node *rnp;
struct rcu_node *rnp_old = NULL;
/* Funnel through hierarchy to reduce memory contention. */
rnp = __this_cpu_read(rsp->rda->mynode);
for (; rnp != NULL; rnp = rnp->parent) {
ret = (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
!raw_spin_trylock(&rnp->fqslock);
if (rnp_old != NULL)
raw_spin_unlock(&rnp_old->fqslock);
if (ret) {
rsp->n_force_qs_lh++;
return;
}
rnp_old = rnp;
}
/* rnp_old == rcu_get_root(rsp), rnp == NULL. */
/* Reached the root of the rcu_node tree, acquire lock. */
raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
raw_spin_unlock(&rnp_old->fqslock);
if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
rsp->n_force_qs_lh++;
raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
return; /* Someone beat us to it. */
}
WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
rcu_gp_kthread_wake(rsp);
}
/*
* This does the RCU core processing work for the specified rcu_state
* and rcu_data structures. This may be called only from the CPU to
* whom the rdp belongs.
*/
static void
__rcu_process_callbacks(struct rcu_state *rsp)
{
unsigned long flags;
bool needwake;
struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
WARN_ON_ONCE(rdp->beenonline == 0);
/* Update RCU state based on any recent quiescent states. */
rcu_check_quiescent_state(rsp, rdp);
/* Does this CPU require a not-yet-started grace period? */
local_irq_save(flags);
if (cpu_needs_another_gp(rsp, rdp)) {
raw_spin_lock_rcu_node(rcu_get_root(rsp)); /* irqs disabled. */
needwake = rcu_start_gp(rsp);
raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags);
if (needwake)
rcu_gp_kthread_wake(rsp);
} else {
local_irq_restore(flags);
}
/* If there are callbacks ready, invoke them. */
if (rcu_segcblist_ready_cbs(&rdp->cblist))
invoke_rcu_callbacks(rsp, rdp);
/* Do any needed deferred wakeups of rcuo kthreads. */
do_nocb_deferred_wakeup(rdp);
}
/*
* Do RCU core processing for the current CPU.
*/
static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
{
struct rcu_state *rsp;
if (cpu_is_offline(smp_processor_id()))
return;
trace_rcu_utilization(TPS("Start RCU core"));
for_each_rcu_flavor(rsp)
__rcu_process_callbacks(rsp);
trace_rcu_utilization(TPS("End RCU core"));
}
/*
* Schedule RCU callback invocation. If the specified type of RCU
* does not support RCU priority boosting, just do a direct call,
* otherwise wake up the per-CPU kernel kthread. Note that because we
* are running on the current CPU with softirqs disabled, the
* rcu_cpu_kthread_task cannot disappear out from under us.
*/
static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
{
if (unlikely(!READ_ONCE(rcu_scheduler_fully_active)))
return;
if (likely(!rsp->boost)) {
rcu_do_batch(rsp, rdp);
return;
}
invoke_rcu_callbacks_kthread();
}
static void invoke_rcu_core(void)
{
if (cpu_online(smp_processor_id()))
raise_softirq(RCU_SOFTIRQ);
}
/*
* Handle any core-RCU processing required by a call_rcu() invocation.
*/
static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
struct rcu_head *head, unsigned long flags)
{
bool needwake;
/*
* If called from an extended quiescent state, invoke the RCU
* core in order to force a re-evaluation of RCU's idleness.
*/
if (!rcu_is_watching())
invoke_rcu_core();
/* If interrupts were disabled or CPU offline, don't invoke RCU core. */
if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
return;
/*
* Force the grace period if too many callbacks or too long waiting.
* Enforce hysteresis, and don't invoke force_quiescent_state()
* if some other CPU has recently done so. Also, don't bother
* invoking force_quiescent_state() if the newly enqueued callback
* is the only one waiting for a grace period to complete.
*/
if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
rdp->qlen_last_fqs_check + qhimark)) {
/* Are we ignoring a completed grace period? */
note_gp_changes(rsp, rdp);
/* Start a new grace period if one not already started. */
if (!rcu_gp_in_progress(rsp)) {
struct rcu_node *rnp_root = rcu_get_root(rsp);
raw_spin_lock_rcu_node(rnp_root);
needwake = rcu_start_gp(rsp);
raw_spin_unlock_rcu_node(rnp_root);
if (needwake)
rcu_gp_kthread_wake(rsp);
} else {
/* Give the grace period a kick. */
rdp->blimit = LONG_MAX;
if (rsp->n_force_qs == rdp->n_force_qs_snap &&
rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
force_quiescent_state(rsp);
rdp->n_force_qs_snap = rsp->n_force_qs;
rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
}
}
}
/*
* RCU callback function to leak a callback.
*/
static void rcu_leak_callback(struct rcu_head *rhp)
{
}
/*
* Helper function for call_rcu() and friends. The cpu argument will
* normally be -1, indicating "currently running CPU". It may specify
* a CPU only if that CPU is a no-CBs CPU. Currently, only _rcu_barrier()
* is expected to specify a CPU.
*/
static void
__call_rcu(struct rcu_head *head, rcu_callback_t func,
struct rcu_state *rsp, int cpu, bool lazy)
{
unsigned long flags;
struct rcu_data *rdp;
/* Misaligned rcu_head! */
WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
if (debug_rcu_head_queue(head)) {
/* Probable double call_rcu(), so leak the callback. */
WRITE_ONCE(head->func, rcu_leak_callback);
WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
return;
}
head->func = func;
head->next = NULL;
local_irq_save(flags);
rdp = this_cpu_ptr(rsp->rda);
/* Add the callback to our list. */
if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist)) || cpu != -1) {
int offline;
if (cpu != -1)
rdp = per_cpu_ptr(rsp->rda, cpu);
if (likely(rdp->mynode)) {
/* Post-boot, so this should be for a no-CBs CPU. */
offline = !__call_rcu_nocb(rdp, head, lazy, flags);
WARN_ON_ONCE(offline);
/* Offline CPU, _call_rcu() illegal, leak callback. */
local_irq_restore(flags);
return;
}
/*
* Very early boot, before rcu_init(). Initialize if needed
* and then drop through to queue the callback.
*/
BUG_ON(cpu != -1);
WARN_ON_ONCE(!rcu_is_watching());
if (rcu_segcblist_empty(&rdp->cblist))
rcu_segcblist_init(&rdp->cblist);
}
rcu_segcblist_enqueue(&rdp->cblist, head, lazy);
if (!lazy)
rcu_idle_count_callbacks_posted();
if (__is_kfree_rcu_offset((unsigned long)func))
trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
rcu_segcblist_n_lazy_cbs(&rdp->cblist),
rcu_segcblist_n_cbs(&rdp->cblist));
else
trace_rcu_callback(rsp->name, head,
rcu_segcblist_n_lazy_cbs(&rdp->cblist),
rcu_segcblist_n_cbs(&rdp->cblist));
/* Go handle any RCU core processing required. */
__call_rcu_core(rsp, rdp, head, flags);
local_irq_restore(flags);
}
/*
* Queue an RCU-sched callback for invocation after a grace period.
*/
void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
{
__call_rcu(head, func, &rcu_sched_state, -1, 0);
}
EXPORT_SYMBOL_GPL(call_rcu_sched);
/*
* Queue an RCU callback for invocation after a quicker grace period.
*/
void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
{
__call_rcu(head, func, &rcu_bh_state, -1, 0);
}
EXPORT_SYMBOL_GPL(call_rcu_bh);
/*
* Queue an RCU callback for lazy invocation after a grace period.
* This will likely be later named something like "call_rcu_lazy()",
* but this change will require some way of tagging the lazy RCU
* callbacks in the list of pending callbacks. Until then, this
* function may only be called from __kfree_rcu().
*/
void kfree_call_rcu(struct rcu_head *head,
rcu_callback_t func)
{
__call_rcu(head, func, rcu_state_p, -1, 1);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);
/*
* Because a context switch is a grace period for RCU-sched and RCU-bh,
* any blocking grace-period wait automatically implies a grace period
* if there is only one CPU online at any point time during execution
* of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
* occasionally incorrectly indicate that there are multiple CPUs online
* when there was in fact only one the whole time, as this just adds
* some overhead: RCU still operates correctly.
*/
static inline int rcu_blocking_is_gp(void)
{
int ret;
might_sleep(); /* Check for RCU read-side critical section. */
preempt_disable();
ret = num_online_cpus() <= 1;
preempt_enable();
return ret;
}
/**
* synchronize_sched - wait until an rcu-sched grace period has elapsed.
*
* Control will return to the caller some time after a full rcu-sched
* grace period has elapsed, in other words after all currently executing
* rcu-sched read-side critical sections have completed. These read-side
* critical sections are delimited by rcu_read_lock_sched() and
* rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
* local_irq_disable(), and so on may be used in place of
* rcu_read_lock_sched().
*
* This means that all preempt_disable code sequences, including NMI and
* non-threaded hardware-interrupt handlers, in progress on entry will
* have completed before this primitive returns. However, this does not
* guarantee that softirq handlers will have completed, since in some
* kernels, these handlers can run in process context, and can block.
*
* Note that this guarantee implies further memory-ordering guarantees.
* On systems with more than one CPU, when synchronize_sched() returns,
* each CPU is guaranteed to have executed a full memory barrier since the
* end of its last RCU-sched read-side critical section whose beginning
* preceded the call to synchronize_sched(). In addition, each CPU having
* an RCU read-side critical section that extends beyond the return from
* synchronize_sched() is guaranteed to have executed a full memory barrier
* after the beginning of synchronize_sched() and before the beginning of
* that RCU read-side critical section. Note that these guarantees include
* CPUs that are offline, idle, or executing in user mode, as well as CPUs
* that are executing in the kernel.
*
* Furthermore, if CPU A invoked synchronize_sched(), which returned
* to its caller on CPU B, then both CPU A and CPU B are guaranteed
* to have executed a full memory barrier during the execution of
* synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
* again only if the system has more than one CPU).
*
* This primitive provides the guarantees made by the (now removed)
* synchronize_kernel() API. In contrast, synchronize_rcu() only
* guarantees that rcu_read_lock() sections will have completed.
* In "classic RCU", these two guarantees happen to be one and
* the same, but can differ in realtime RCU implementations.
*/
void synchronize_sched(void)
{
RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
lock_is_held(&rcu_lock_map) ||
lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_sched() in RCU-sched read-side critical section");
if (rcu_blocking_is_gp())
return;
if (rcu_gp_is_expedited())
synchronize_sched_expedited();
else
wait_rcu_gp(call_rcu_sched);
}
EXPORT_SYMBOL_GPL(synchronize_sched);
/**
* synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
*
* Control will return to the caller some time after a full rcu_bh grace
* period has elapsed, in other words after all currently executing rcu_bh
* read-side critical sections have completed. RCU read-side critical
* sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
* and may be nested.
*
* See the description of synchronize_sched() for more detailed information
* on memory ordering guarantees.
*/
void synchronize_rcu_bh(void)
{
RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
lock_is_held(&rcu_lock_map) ||
lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
if (rcu_blocking_is_gp())
return;
if (rcu_gp_is_expedited())
synchronize_rcu_bh_expedited();
else
wait_rcu_gp(call_rcu_bh);
}
EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
/**
* get_state_synchronize_rcu - Snapshot current RCU state
*
* Returns a cookie that is used by a later call to cond_synchronize_rcu()
* to determine whether or not a full grace period has elapsed in the
* meantime.
*/
unsigned long get_state_synchronize_rcu(void)
{
/*
* Any prior manipulation of RCU-protected data must happen
* before the load from ->gpnum.
*/
smp_mb(); /* ^^^ */
/*
* Make sure this load happens before the purportedly
* time-consuming work between get_state_synchronize_rcu()
* and cond_synchronize_rcu().
*/
return smp_load_acquire(&rcu_state_p->gpnum);
}
EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
/**
* cond_synchronize_rcu - Conditionally wait for an RCU grace period
*
* @oldstate: return value from earlier call to get_state_synchronize_rcu()
*
* If a full RCU grace period has elapsed since the earlier call to
* get_state_synchronize_rcu(), just return. Otherwise, invoke
* synchronize_rcu() to wait for a full grace period.
*
* Yes, this function does not take counter wrap into account. But
* counter wrap is harmless. If the counter wraps, we have waited for
* more than 2 billion grace periods (and way more on a 64-bit system!),
* so waiting for one additional grace period should be just fine.
*/
void cond_synchronize_rcu(unsigned long oldstate)
{
unsigned long newstate;
/*
* Ensure that this load happens before any RCU-destructive
* actions the caller might carry out after we return.
*/
newstate = smp_load_acquire(&rcu_state_p->completed);
if (ULONG_CMP_GE(oldstate, newstate))
synchronize_rcu();
}
EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
/**
* get_state_synchronize_sched - Snapshot current RCU-sched state
*
* Returns a cookie that is used by a later call to cond_synchronize_sched()
* to determine whether or not a full grace period has elapsed in the
* meantime.
*/
unsigned long get_state_synchronize_sched(void)
{
/*
* Any prior manipulation of RCU-protected data must happen
* before the load from ->gpnum.
*/
smp_mb(); /* ^^^ */
/*
* Make sure this load happens before the purportedly
* time-consuming work between get_state_synchronize_sched()
* and cond_synchronize_sched().
*/
return smp_load_acquire(&rcu_sched_state.gpnum);
}
EXPORT_SYMBOL_GPL(get_state_synchronize_sched);
/**
* cond_synchronize_sched - Conditionally wait for an RCU-sched grace period
*
* @oldstate: return value from earlier call to get_state_synchronize_sched()
*
* If a full RCU-sched grace period has elapsed since the earlier call to
* get_state_synchronize_sched(), just return. Otherwise, invoke
* synchronize_sched() to wait for a full grace period.
*
* Yes, this function does not take counter wrap into account. But
* counter wrap is harmless. If the counter wraps, we have waited for
* more than 2 billion grace periods (and way more on a 64-bit system!),
* so waiting for one additional grace period should be just fine.
*/
void cond_synchronize_sched(unsigned long oldstate)
{
unsigned long newstate;
/*
* Ensure that this load happens before any RCU-destructive
* actions the caller might carry out after we return.
*/
newstate = smp_load_acquire(&rcu_sched_state.completed);
if (ULONG_CMP_GE(oldstate, newstate))
synchronize_sched();
}
EXPORT_SYMBOL_GPL(cond_synchronize_sched);
/*
* Check to see if there is any immediate RCU-related work to be done
* by the current CPU, for the specified type of RCU, returning 1 if so.
* The checks are in order of increasing expense: checks that can be
* carried out against CPU-local state are performed first. However,
* we must check for CPU stalls first, else we might not get a chance.
*/
static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
{
struct rcu_node *rnp = rdp->mynode;
rdp->n_rcu_pending++;
/* Check for CPU stalls, if enabled. */
check_cpu_stall(rsp, rdp);
/* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
if (rcu_nohz_full_cpu(rsp))
return 0;
/* Is the RCU core waiting for a quiescent state from this CPU? */
if (rcu_scheduler_fully_active &&
rdp->core_needs_qs && rdp->cpu_no_qs.b.norm &&
rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_dynticks.rcu_qs_ctr)) {
rdp->n_rp_core_needs_qs++;
} else if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm) {
rdp->n_rp_report_qs++;
return 1;
}
/* Does this CPU have callbacks ready to invoke? */
if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
rdp->n_rp_cb_ready++;
return 1;
}
/* Has RCU gone idle with this CPU needing another grace period? */
if (cpu_needs_another_gp(rsp, rdp)) {
rdp->n_rp_cpu_needs_gp++;
return 1;
}
/* Has another RCU grace period completed? */
if (READ_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
rdp->n_rp_gp_completed++;
return 1;
}
/* Has a new RCU grace period started? */
if (READ_ONCE(rnp->gpnum) != rdp->gpnum ||
unlikely(READ_ONCE(rdp->gpwrap))) { /* outside lock */
rdp->n_rp_gp_started++;
return 1;
}
/* Does this CPU need a deferred NOCB wakeup? */
if (rcu_nocb_need_deferred_wakeup(rdp)) {
rdp->n_rp_nocb_defer_wakeup++;
return 1;
}
/* nothing to do */
rdp->n_rp_need_nothing++;
return 0;
}
/*
* Check to see if there is any immediate RCU-related work to be done
* by the current CPU, returning 1 if so. This function is part of the
* RCU implementation; it is -not- an exported member of the RCU API.
*/
static int rcu_pending(void)
{
struct rcu_state *rsp;
for_each_rcu_flavor(rsp)
if (__rcu_pending(rsp, this_cpu_ptr(rsp->rda)))
return 1;
return 0;
}
/*
* Return true if the specified CPU has any callback. If all_lazy is
* non-NULL, store an indication of whether all callbacks are lazy.
* (If there are no callbacks, all of them are deemed to be lazy.)
*/
static bool __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy)
{
bool al = true;
bool hc = false;
struct rcu_data *rdp;
struct rcu_state *rsp;
for_each_rcu_flavor(rsp) {
rdp = this_cpu_ptr(rsp->rda);
if (rcu_segcblist_empty(&rdp->cblist))
continue;
hc = true;
if (rcu_segcblist_n_nonlazy_cbs(&rdp->cblist) || !all_lazy) {
al = false;
break;
}
}
if (all_lazy)
*all_lazy = al;
return hc;
}
/*
* Helper function for _rcu_barrier() tracing. If tracing is disabled,
* the compiler is expected to optimize this away.
*/
static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
int cpu, unsigned long done)
{
trace_rcu_barrier(rsp->name, s, cpu,
atomic_read(&rsp->barrier_cpu_count), done);
}
/*
* RCU callback function for _rcu_barrier(). If we are last, wake
* up the task executing _rcu_barrier().
*/
static void rcu_barrier_callback(struct rcu_head *rhp)
{
struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
struct rcu_state *rsp = rdp->rsp;
if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
_rcu_barrier_trace(rsp, "LastCB", -1, rsp->barrier_sequence);
complete(&rsp->barrier_completion);
} else {
_rcu_barrier_trace(rsp, "CB", -1, rsp->barrier_sequence);
}
}
/*
* Called with preemption disabled, and from cross-cpu IRQ context.
*/
static void rcu_barrier_func(void *type)
{
struct rcu_state *rsp = type;
struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
_rcu_barrier_trace(rsp, "IRQ", -1, rsp->barrier_sequence);
atomic_inc(&rsp->barrier_cpu_count);
rsp->call(&rdp->barrier_head, rcu_barrier_callback);
}
/*
* Orchestrate the specified type of RCU barrier, waiting for all
* RCU callbacks of the specified type to complete.
*/
static void _rcu_barrier(struct rcu_state *rsp)
{
int cpu;
struct rcu_data *rdp;
unsigned long s = rcu_seq_snap(&rsp->barrier_sequence);
_rcu_barrier_trace(rsp, "Begin", -1, s);
/* Take mutex to serialize concurrent rcu_barrier() requests. */
mutex_lock(&rsp->barrier_mutex);
/* Did someone else do our work for us? */
if (rcu_seq_done(&rsp->barrier_sequence, s)) {
_rcu_barrier_trace(rsp, "EarlyExit", -1, rsp->barrier_sequence);
smp_mb(); /* caller's subsequent code after above check. */
mutex_unlock(&rsp->barrier_mutex);
return;
}
/* Mark the start of the barrier operation. */
rcu_seq_start(&rsp->barrier_sequence);
_rcu_barrier_trace(rsp, "Inc1", -1, rsp->barrier_sequence);
/*
* Initialize the count to one rather than to zero in order to
* avoid a too-soon return to zero in case of a short grace period
* (or preemption of this task). Exclude CPU-hotplug operations
* to ensure that no offline CPU has callbacks queued.
*/
init_completion(&rsp->barrier_completion);
atomic_set(&rsp->barrier_cpu_count, 1);
get_online_cpus();
/*
* Force each CPU with callbacks to register a new callback.
* When that callback is invoked, we will know that all of the
* corresponding CPU's preceding callbacks have been invoked.
*/
for_each_possible_cpu(cpu) {
if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
continue;
rdp = per_cpu_ptr(rsp->rda, cpu);
if (rcu_is_nocb_cpu(cpu)) {
if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) {
_rcu_barrier_trace(rsp, "OfflineNoCB", cpu,
rsp->barrier_sequence);
} else {
_rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
rsp->barrier_sequence);
smp_mb__before_atomic();
atomic_inc(&rsp->barrier_cpu_count);
__call_rcu(&rdp->barrier_head,
rcu_barrier_callback, rsp, cpu, 0);
}
} else if (rcu_segcblist_n_cbs(&rdp->cblist)) {
_rcu_barrier_trace(rsp, "OnlineQ", cpu,
rsp->barrier_sequence);
smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
} else {
_rcu_barrier_trace(rsp, "OnlineNQ", cpu,
rsp->barrier_sequence);
}
}
put_online_cpus();
/*
* Now that we have an rcu_barrier_callback() callback on each
* CPU, and thus each counted, remove the initial count.
*/
if (atomic_dec_and_test(&rsp->barrier_cpu_count))
complete(&rsp->barrier_completion);
/* Wait for all rcu_barrier_callback() callbacks to be invoked. */
wait_for_completion(&rsp->barrier_completion);
/* Mark the end of the barrier operation. */
_rcu_barrier_trace(rsp, "Inc2", -1, rsp->barrier_sequence);
rcu_seq_end(&rsp->barrier_sequence);
/* Other rcu_barrier() invocations can now safely proceed. */
mutex_unlock(&rsp->barrier_mutex);
}
/**
* rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
*/
void rcu_barrier_bh(void)
{
_rcu_barrier(&rcu_bh_state);
}
EXPORT_SYMBOL_GPL(rcu_barrier_bh);
/**
* rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
*/
void rcu_barrier_sched(void)
{
_rcu_barrier(&rcu_sched_state);
}
EXPORT_SYMBOL_GPL(rcu_barrier_sched);
/*
* Propagate ->qsinitmask bits up the rcu_node tree to account for the
* first CPU in a given leaf rcu_node structure coming online. The caller
* must hold the corresponding leaf rcu_node ->lock with interrrupts
* disabled.
*/
static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
{
long mask;
struct rcu_node *rnp = rnp_leaf;
for (;;) {
mask = rnp->grpmask;
rnp = rnp->parent;
if (rnp == NULL)
return;
raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
rnp->qsmaskinit |= mask;
raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
}
}
/*
* Do boot-time initialization of a CPU's per-CPU RCU data.
*/
static void __init
rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
{
unsigned long flags;
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_node *rnp = rcu_get_root(rsp);
/* Set up local state, ensuring consistent view of global state. */
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp->dynticks)));
rdp->cpu = cpu;
rdp->rsp = rsp;
rcu_boot_init_nocb_percpu_data(rdp);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
/*
* Initialize a CPU's per-CPU RCU data. Note that only one online or
* offline event can be happening at a given time. Note also that we
* can accept some slop in the rsp->completed access due to the fact
* that this CPU cannot possibly have any RCU callbacks in flight yet.
*/
static void
rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
{
unsigned long flags;
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_node *rnp = rcu_get_root(rsp);
/* Set up local state, ensuring consistent view of global state. */
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rdp->qlen_last_fqs_check = 0;
rdp->n_force_qs_snap = rsp->n_force_qs;
rdp->blimit = blimit;
if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */
!init_nocb_callback_list(rdp))
rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
rcu_sysidle_init_percpu_data(rdp->dynticks);
rcu_dynticks_eqs_online();
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
/*
* Add CPU to leaf rcu_node pending-online bitmask. Any needed
* propagation up the rcu_node tree will happen at the beginning
* of the next grace period.
*/
rnp = rdp->mynode;
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
if (!rdp->beenonline)
WRITE_ONCE(rsp->ncpus, READ_ONCE(rsp->ncpus) + 1);
rdp->beenonline = true; /* We have now been online. */
rdp->gpnum = rnp->completed; /* Make CPU later note any new GP. */
rdp->completed = rnp->completed;
rdp->cpu_no_qs.b.norm = true;
rdp->rcu_qs_ctr_snap = per_cpu(rcu_dynticks.rcu_qs_ctr, cpu);
rdp->core_needs_qs = false;
trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
int rcutree_prepare_cpu(unsigned int cpu)
{
struct rcu_state *rsp;
for_each_rcu_flavor(rsp)
rcu_init_percpu_data(cpu, rsp);
rcu_prepare_kthreads(cpu);
rcu_spawn_all_nocb_kthreads(cpu);
return 0;
}
static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
{
struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
}
int rcutree_online_cpu(unsigned int cpu)
{
sync_sched_exp_online_cleanup(cpu);
rcutree_affinity_setting(cpu, -1);
return 0;
}
int rcutree_offline_cpu(unsigned int cpu)
{
rcutree_affinity_setting(cpu, cpu);
return 0;
}
int rcutree_dying_cpu(unsigned int cpu)
{
struct rcu_state *rsp;
for_each_rcu_flavor(rsp)
rcu_cleanup_dying_cpu(rsp);
return 0;
}
int rcutree_dead_cpu(unsigned int cpu)
{
struct rcu_state *rsp;
for_each_rcu_flavor(rsp) {
rcu_cleanup_dead_cpu(cpu, rsp);
do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
}
return 0;
}
/*
* Mark the specified CPU as being online so that subsequent grace periods
* (both expedited and normal) will wait on it. Note that this means that
* incoming CPUs are not allowed to use RCU read-side critical sections
* until this function is called. Failing to observe this restriction
* will result in lockdep splats.
*/
void rcu_cpu_starting(unsigned int cpu)
{
unsigned long flags;
unsigned long mask;
struct rcu_data *rdp;
struct rcu_node *rnp;
struct rcu_state *rsp;
for_each_rcu_flavor(rsp) {
rdp = per_cpu_ptr(rsp->rda, cpu);
rnp = rdp->mynode;
mask = rdp->grpmask;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rnp->qsmaskinitnext |= mask;
rnp->expmaskinitnext |= mask;
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
}
#ifdef CONFIG_HOTPLUG_CPU
/*
* The CPU is exiting the idle loop into the arch_cpu_idle_dead()
* function. We now remove it from the rcu_node tree's ->qsmaskinit
* bit masks.
* The CPU is exiting the idle loop into the arch_cpu_idle_dead()
* function. We now remove it from the rcu_node tree's ->qsmaskinit
* bit masks.
*/
static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp)
{
unsigned long flags;
unsigned long mask;
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
/* Remove outgoing CPU from mask in the leaf rcu_node structure. */
mask = rdp->grpmask;
raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
rnp->qsmaskinitnext &= ~mask;
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
void rcu_report_dead(unsigned int cpu)
{
struct rcu_state *rsp;
/* QS for any half-done expedited RCU-sched GP. */
preempt_disable();
rcu_report_exp_rdp(&rcu_sched_state,
this_cpu_ptr(rcu_sched_state.rda), true);
preempt_enable();
for_each_rcu_flavor(rsp)
rcu_cleanup_dying_idle_cpu(cpu, rsp);
}
#endif
static int rcu_pm_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
switch (action) {
case PM_HIBERNATION_PREPARE:
case PM_SUSPEND_PREPARE:
if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
rcu_expedite_gp();
break;
case PM_POST_HIBERNATION:
case PM_POST_SUSPEND:
if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
rcu_unexpedite_gp();
break;
default:
break;
}
return NOTIFY_OK;
}
/*
* Spawn the kthreads that handle each RCU flavor's grace periods.
*/
static int __init rcu_spawn_gp_kthread(void)
{
unsigned long flags;
int kthread_prio_in = kthread_prio;
struct rcu_node *rnp;
struct rcu_state *rsp;
struct sched_param sp;
struct task_struct *t;
/* Force priority into range. */
if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
kthread_prio = 1;
else if (kthread_prio < 0)
kthread_prio = 0;
else if (kthread_prio > 99)
kthread_prio = 99;
if (kthread_prio != kthread_prio_in)
pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
kthread_prio, kthread_prio_in);
rcu_scheduler_fully_active = 1;
for_each_rcu_flavor(rsp) {
t = kthread_create(rcu_gp_kthread, rsp, "%s", rsp->name);
BUG_ON(IS_ERR(t));
rnp = rcu_get_root(rsp);
raw_spin_lock_irqsave_rcu_node(rnp, flags);
rsp->gp_kthread = t;
if (kthread_prio) {
sp.sched_priority = kthread_prio;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
wake_up_process(t);
}
rcu_spawn_nocb_kthreads();
rcu_spawn_boost_kthreads();
return 0;
}
early_initcall(rcu_spawn_gp_kthread);
/*
* This function is invoked towards the end of the scheduler's
* initialization process. Before this is called, the idle task might
* contain synchronous grace-period primitives (during which time, this idle
* task is booting the system, and such primitives are no-ops). After this
* function is called, any synchronous grace-period primitives are run as
* expedited, with the requesting task driving the grace period forward.
* A later core_initcall() rcu_set_runtime_mode() will switch to full
* runtime RCU functionality.
*/
void rcu_scheduler_starting(void)
{
WARN_ON(num_online_cpus() != 1);
WARN_ON(nr_context_switches() > 0);
rcu_test_sync_prims();
rcu_scheduler_active = RCU_SCHEDULER_INIT;
rcu_test_sync_prims();
}
/*
* Helper function for rcu_init() that initializes one rcu_state structure.
*/
static void __init rcu_init_one(struct rcu_state *rsp)
{
static const char * const buf[] = RCU_NODE_NAME_INIT;
static const char * const fqs[] = RCU_FQS_NAME_INIT;
static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
int cpustride = 1;
int i;
int j;
struct rcu_node *rnp;
BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
/* Silence gcc 4.8 false positive about array index out of range. */
if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
panic("rcu_init_one: rcu_num_lvls out of range");
/* Initialize the level-tracking arrays. */
for (i = 1; i < rcu_num_lvls; i++)
rsp->level[i] = rsp->level[i - 1] + num_rcu_lvl[i - 1];
rcu_init_levelspread(levelspread, num_rcu_lvl);
/* Initialize the elements themselves, starting from the leaves. */
for (i = rcu_num_lvls - 1; i >= 0; i--) {
cpustride *= levelspread[i];
rnp = rsp->level[i];
for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
&rcu_node_class[i], buf[i]);
raw_spin_lock_init(&rnp->fqslock);
lockdep_set_class_and_name(&rnp->fqslock,
&rcu_fqs_class[i], fqs[i]);
rnp->gpnum = rsp->gpnum;
rnp->completed = rsp->completed;
rnp->qsmask = 0;
rnp->qsmaskinit = 0;
rnp->grplo = j * cpustride;
rnp->grphi = (j + 1) * cpustride - 1;
if (rnp->grphi >= nr_cpu_ids)
rnp->grphi = nr_cpu_ids - 1;
if (i == 0) {
rnp->grpnum = 0;
rnp->grpmask = 0;
rnp->parent = NULL;
} else {
rnp->grpnum = j % levelspread[i - 1];
rnp->grpmask = 1UL << rnp->grpnum;
rnp->parent = rsp->level[i - 1] +
j / levelspread[i - 1];
}
rnp->level = i;
INIT_LIST_HEAD(&rnp->blkd_tasks);
rcu_init_one_nocb(rnp);
init_waitqueue_head(&rnp->exp_wq[0]);
init_waitqueue_head(&rnp->exp_wq[1]);
init_waitqueue_head(&rnp->exp_wq[2]);
init_waitqueue_head(&rnp->exp_wq[3]);
spin_lock_init(&rnp->exp_lock);
}
}
init_swait_queue_head(&rsp->gp_wq);
init_swait_queue_head(&rsp->expedited_wq);
rnp = rsp->level[rcu_num_lvls - 1];
for_each_possible_cpu(i) {
while (i > rnp->grphi)
rnp++;
per_cpu_ptr(rsp->rda, i)->mynode = rnp;
rcu_boot_init_percpu_data(i, rsp);
}
list_add(&rsp->flavors, &rcu_struct_flavors);
}
/*
* Compute the rcu_node tree geometry from kernel parameters. This cannot
* replace the definitions in tree.h because those are needed to size
* the ->node array in the rcu_state structure.
*/
static void __init rcu_init_geometry(void)
{
ulong d;
int i;
int rcu_capacity[RCU_NUM_LVLS];
/*
* Initialize any unspecified boot parameters.
* The default values of jiffies_till_first_fqs and
* jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
* value, which is a function of HZ, then adding one for each
* RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
*/
d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
if (jiffies_till_first_fqs == ULONG_MAX)
jiffies_till_first_fqs = d;
if (jiffies_till_next_fqs == ULONG_MAX)
jiffies_till_next_fqs = d;
/* If the compile-time values are accurate, just leave. */
if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
nr_cpu_ids == NR_CPUS)
return;
pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
rcu_fanout_leaf, nr_cpu_ids);
/*
* The boot-time rcu_fanout_leaf parameter must be at least two
* and cannot exceed the number of bits in the rcu_node masks.
* Complain and fall back to the compile-time values if this
* limit is exceeded.
*/
if (rcu_fanout_leaf < 2 ||
rcu_fanout_leaf > sizeof(unsigned long) * 8) {
rcu_fanout_leaf = RCU_FANOUT_LEAF;
WARN_ON(1);
return;
}
/*
* Compute number of nodes that can be handled an rcu_node tree
* with the given number of levels.
*/
rcu_capacity[0] = rcu_fanout_leaf;
for (i = 1; i < RCU_NUM_LVLS; i++)
rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
/*
* The tree must be able to accommodate the configured number of CPUs.
* If this limit is exceeded, fall back to the compile-time values.
*/
if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
rcu_fanout_leaf = RCU_FANOUT_LEAF;
WARN_ON(1);
return;
}
/* Calculate the number of levels in the tree. */
for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
}
rcu_num_lvls = i + 1;
/* Calculate the number of rcu_nodes at each level of the tree. */
for (i = 0; i < rcu_num_lvls; i++) {
int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
}
/* Calculate the total number of rcu_node structures. */
rcu_num_nodes = 0;
for (i = 0; i < rcu_num_lvls; i++)
rcu_num_nodes += num_rcu_lvl[i];
}
/*
* Dump out the structure of the rcu_node combining tree associated
* with the rcu_state structure referenced by rsp.
*/
static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp)
{
int level = 0;
struct rcu_node *rnp;
pr_info("rcu_node tree layout dump\n");
pr_info(" ");
rcu_for_each_node_breadth_first(rsp, rnp) {
if (rnp->level != level) {
pr_cont("\n");
pr_info(" ");
level = rnp->level;
}
pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum);
}
pr_cont("\n");
}
void __init rcu_init(void)
{
int cpu;
rcu_early_boot_tests();
rcu_bootup_announce();
rcu_init_geometry();
rcu_init_one(&rcu_bh_state);
rcu_init_one(&rcu_sched_state);
if (dump_tree)
rcu_dump_rcu_node_tree(&rcu_sched_state);
__rcu_init_preempt();
open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
/*
* We don't need protection against CPU-hotplug here because
* this is called early in boot, before either interrupts
* or the scheduler are operational.
*/
pm_notifier(rcu_pm_notify, 0);
for_each_online_cpu(cpu) {
rcutree_prepare_cpu(cpu);
rcu_cpu_starting(cpu);
}
}
#include "tree_exp.h"
#include "tree_plugin.h"
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