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Diffstat (limited to 'kernel/rcupreempt.c')
| -rw-r--r-- | kernel/rcupreempt.c | 1482 |
1 files changed, 1482 insertions, 0 deletions
diff --git a/kernel/rcupreempt.c b/kernel/rcupreempt.c new file mode 100644 index 0000000..59236e8 --- /dev/null +++ b/kernel/rcupreempt.c @@ -0,0 +1,1482 @@ +/* + * Read-Copy Update mechanism for mutual exclusion, realtime implementation + * + * 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, write to the Free Software + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * + * Copyright IBM Corporation, 2006 + * + * Authors: Paul E. McKenney <paulmck@us.ibm.com> + * With thanks to Esben Nielsen, Bill Huey, and Ingo Molnar + * for pushing me away from locks and towards counters, and + * to Suparna Bhattacharya for pushing me completely away + * from atomic instructions on the read side. + * + * - Added handling of Dynamic Ticks + * Copyright 2007 - Paul E. Mckenney <paulmck@us.ibm.com> + * - Steven Rostedt <srostedt@redhat.com> + * + * Papers: http://www.rdrop.com/users/paulmck/RCU + * + * Design Document: http://lwn.net/Articles/253651/ + * + * For detailed explanation of Read-Copy Update mechanism see - + * Documentation/RCU/ *.txt + * + */ +#include <linux/types.h> +#include <linux/kernel.h> +#include <linux/init.h> +#include <linux/spinlock.h> +#include <linux/smp.h> +#include <linux/rcupdate.h> +#include <linux/interrupt.h> +#include <linux/sched.h> +#include <asm/atomic.h> +#include <linux/bitops.h> +#include <linux/module.h> +#include <linux/kthread.h> +#include <linux/completion.h> +#include <linux/moduleparam.h> +#include <linux/percpu.h> +#include <linux/notifier.h> +#include <linux/cpu.h> +#include <linux/random.h> +#include <linux/delay.h> +#include <linux/cpumask.h> +#include <linux/rcupreempt_trace.h> +#include <asm/byteorder.h> + +/* + * PREEMPT_RCU data structures. + */ + +/* + * GP_STAGES specifies the number of times the state machine has + * to go through the all the rcu_try_flip_states (see below) + * in a single Grace Period. + * + * GP in GP_STAGES stands for Grace Period ;) + */ +#define GP_STAGES 2 +struct rcu_data { + spinlock_t lock; /* Protect rcu_data fields. */ + long completed; /* Number of last completed batch. */ + int waitlistcount; + struct rcu_head *nextlist; + struct rcu_head **nexttail; + struct rcu_head *waitlist[GP_STAGES]; + struct rcu_head **waittail[GP_STAGES]; + struct rcu_head *donelist; /* from waitlist & waitschedlist */ + struct rcu_head **donetail; + long rcu_flipctr[2]; + struct rcu_head *nextschedlist; + struct rcu_head **nextschedtail; + struct rcu_head *waitschedlist; + struct rcu_head **waitschedtail; + int rcu_sched_sleeping; +#ifdef CONFIG_RCU_TRACE + struct rcupreempt_trace trace; +#endif /* #ifdef CONFIG_RCU_TRACE */ +}; + +/* + * States for rcu_try_flip() and friends. + */ + +enum rcu_try_flip_states { + + /* + * Stay here if nothing is happening. Flip the counter if somthing + * starts happening. Denoted by "I" + */ + rcu_try_flip_idle_state, + + /* + * Wait here for all CPUs to notice that the counter has flipped. This + * prevents the old set of counters from ever being incremented once + * we leave this state, which in turn is necessary because we cannot + * test any individual counter for zero -- we can only check the sum. + * Denoted by "A". + */ + rcu_try_flip_waitack_state, + + /* + * Wait here for the sum of the old per-CPU counters to reach zero. + * Denoted by "Z". + */ + rcu_try_flip_waitzero_state, + + /* + * Wait here for each of the other CPUs to execute a memory barrier. + * This is necessary to ensure that these other CPUs really have + * completed executing their RCU read-side critical sections, despite + * their CPUs wildly reordering memory. Denoted by "M". + */ + rcu_try_flip_waitmb_state, +}; + +/* + * States for rcu_ctrlblk.rcu_sched_sleep. + */ + +enum rcu_sched_sleep_states { + rcu_sched_not_sleeping, /* Not sleeping, callbacks need GP. */ + rcu_sched_sleep_prep, /* Thinking of sleeping, rechecking. */ + rcu_sched_sleeping, /* Sleeping, awaken if GP needed. */ +}; + +struct rcu_ctrlblk { + spinlock_t fliplock; /* Protect state-machine transitions. */ + long completed; /* Number of last completed batch. */ + enum rcu_try_flip_states rcu_try_flip_state; /* The current state of + the rcu state machine */ + spinlock_t schedlock; /* Protect rcu_sched sleep state. */ + enum rcu_sched_sleep_states sched_sleep; /* rcu_sched state. */ + wait_queue_head_t sched_wq; /* Place for rcu_sched to sleep. */ +}; + +static DEFINE_PER_CPU(struct rcu_data, rcu_data); +static struct rcu_ctrlblk rcu_ctrlblk = { + .fliplock = __SPIN_LOCK_UNLOCKED(rcu_ctrlblk.fliplock), + .completed = 0, + .rcu_try_flip_state = rcu_try_flip_idle_state, + .schedlock = __SPIN_LOCK_UNLOCKED(rcu_ctrlblk.schedlock), + .sched_sleep = rcu_sched_not_sleeping, + .sched_wq = __WAIT_QUEUE_HEAD_INITIALIZER(rcu_ctrlblk.sched_wq), +}; + +static struct task_struct *rcu_sched_grace_period_task; + +#ifdef CONFIG_RCU_TRACE +static char *rcu_try_flip_state_names[] = + { "idle", "waitack", "waitzero", "waitmb" }; +#endif /* #ifdef CONFIG_RCU_TRACE */ + +static cpumask_t rcu_cpu_online_map __read_mostly = CPU_MASK_NONE; + +/* + * Enum and per-CPU flag to determine when each CPU has seen + * the most recent counter flip. + */ + +enum rcu_flip_flag_values { + rcu_flip_seen, /* Steady/initial state, last flip seen. */ + /* Only GP detector can update. */ + rcu_flipped /* Flip just completed, need confirmation. */ + /* Only corresponding CPU can update. */ +}; +static DEFINE_PER_CPU_SHARED_ALIGNED(enum rcu_flip_flag_values, rcu_flip_flag) + = rcu_flip_seen; + +/* + * Enum and per-CPU flag to determine when each CPU has executed the + * needed memory barrier to fence in memory references from its last RCU + * read-side critical section in the just-completed grace period. + */ + +enum rcu_mb_flag_values { + rcu_mb_done, /* Steady/initial state, no mb()s required. */ + /* Only GP detector can update. */ + rcu_mb_needed /* Flip just completed, need an mb(). */ + /* Only corresponding CPU can update. */ +}; +static DEFINE_PER_CPU_SHARED_ALIGNED(enum rcu_mb_flag_values, rcu_mb_flag) + = rcu_mb_done; + +/* + * RCU_DATA_ME: find the current CPU's rcu_data structure. + * RCU_DATA_CPU: find the specified CPU's rcu_data structure. + */ +#define RCU_DATA_ME() (&__get_cpu_var(rcu_data)) +#define RCU_DATA_CPU(cpu) (&per_cpu(rcu_data, cpu)) + +/* + * Helper macro for tracing when the appropriate rcu_data is not + * cached in a local variable, but where the CPU number is so cached. + */ +#define RCU_TRACE_CPU(f, cpu) RCU_TRACE(f, &(RCU_DATA_CPU(cpu)->trace)); + +/* + * Helper macro for tracing when the appropriate rcu_data is not + * cached in a local variable. + */ +#define RCU_TRACE_ME(f) RCU_TRACE(f, &(RCU_DATA_ME()->trace)); + +/* + * Helper macro for tracing when the appropriate rcu_data is pointed + * to by a local variable. + */ +#define RCU_TRACE_RDP(f, rdp) RCU_TRACE(f, &((rdp)->trace)); + +#define RCU_SCHED_BATCH_TIME (HZ / 50) + +/* + * Return the number of RCU batches processed thus far. Useful + * for debug and statistics. + */ +long rcu_batches_completed(void) +{ + return rcu_ctrlblk.completed; +} +EXPORT_SYMBOL_GPL(rcu_batches_completed); + +void __rcu_read_lock(void) +{ + int idx; + struct task_struct *t = current; + int nesting; + + nesting = ACCESS_ONCE(t->rcu_read_lock_nesting); + if (nesting != 0) { + + /* An earlier rcu_read_lock() covers us, just count it. */ + + t->rcu_read_lock_nesting = nesting + 1; + + } else { + unsigned long flags; + + /* + * We disable interrupts for the following reasons: + * - If we get scheduling clock interrupt here, and we + * end up acking the counter flip, it's like a promise + * that we will never increment the old counter again. + * Thus we will break that promise if that + * scheduling clock interrupt happens between the time + * we pick the .completed field and the time that we + * increment our counter. + * + * - We don't want to be preempted out here. + * + * NMIs can still occur, of course, and might themselves + * contain rcu_read_lock(). + */ + + local_irq_save(flags); + + /* + * Outermost nesting of rcu_read_lock(), so increment + * the current counter for the current CPU. Use volatile + * casts to prevent the compiler from reordering. + */ + + idx = ACCESS_ONCE(rcu_ctrlblk.completed) & 0x1; + ACCESS_ONCE(RCU_DATA_ME()->rcu_flipctr[idx])++; + + /* + * Now that the per-CPU counter has been incremented, we + * are protected from races with rcu_read_lock() invoked + * from NMI handlers on this CPU. We can therefore safely + * increment the nesting counter, relieving further NMIs + * of the need to increment the per-CPU counter. + */ + + ACCESS_ONCE(t->rcu_read_lock_nesting) = nesting + 1; + + /* + * Now that we have preventing any NMIs from storing + * to the ->rcu_flipctr_idx, we can safely use it to + * remember which counter to decrement in the matching + * rcu_read_unlock(). + */ + + ACCESS_ONCE(t->rcu_flipctr_idx) = idx; + local_irq_restore(flags); + } +} +EXPORT_SYMBOL_GPL(__rcu_read_lock); + +void __rcu_read_unlock(void) +{ + int idx; + struct task_struct *t = current; + int nesting; + + nesting = ACCESS_ONCE(t->rcu_read_lock_nesting); + if (nesting > 1) { + + /* + * We are still protected by the enclosing rcu_read_lock(), + * so simply decrement the counter. + */ + + t->rcu_read_lock_nesting = nesting - 1; + + } else { + unsigned long flags; + + /* + * Disable local interrupts to prevent the grace-period + * detection state machine from seeing us half-done. + * NMIs can still occur, of course, and might themselves + * contain rcu_read_lock() and rcu_read_unlock(). + */ + + local_irq_save(flags); + + /* + * Outermost nesting of rcu_read_unlock(), so we must + * decrement the current counter for the current CPU. + * This must be done carefully, because NMIs can + * occur at any point in this code, and any rcu_read_lock() + * and rcu_read_unlock() pairs in the NMI handlers + * must interact non-destructively with this code. + * Lots of volatile casts, and -very- careful ordering. + * + * Changes to this code, including this one, must be + * inspected, validated, and tested extremely carefully!!! + */ + + /* + * First, pick up the index. + */ + + idx = ACCESS_ONCE(t->rcu_flipctr_idx); + + /* + * Now that we have fetched the counter index, it is + * safe to decrement the per-task RCU nesting counter. + * After this, any interrupts or NMIs will increment and + * decrement the per-CPU counters. + */ + ACCESS_ONCE(t->rcu_read_lock_nesting) = nesting - 1; + + /* + * It is now safe to decrement this task's nesting count. + * NMIs that occur after this statement will route their + * rcu_read_lock() calls through this "else" clause, and + * will thus start incrementing the per-CPU counter on + * their own. They will also clobber ->rcu_flipctr_idx, + * but that is OK, since we have already fetched it. + */ + + ACCESS_ONCE(RCU_DATA_ME()->rcu_flipctr[idx])--; + local_irq_restore(flags); + } +} +EXPORT_SYMBOL_GPL(__rcu_read_unlock); + +/* + * If a global counter flip has occurred since the last time that we + * advanced callbacks, advance them. Hardware interrupts must be + * disabled when calling this function. + */ +static void __rcu_advance_callbacks(struct rcu_data *rdp) +{ + int cpu; + int i; + int wlc = 0; + + if (rdp->completed != rcu_ctrlblk.completed) { + if (rdp->waitlist[GP_STAGES - 1] != NULL) { + *rdp->donetail = rdp->waitlist[GP_STAGES - 1]; + rdp->donetail = rdp->waittail[GP_STAGES - 1]; + RCU_TRACE_RDP(rcupreempt_trace_move2done, rdp); + } + for (i = GP_STAGES - 2; i >= 0; i--) { + if (rdp->waitlist[i] != NULL) { + rdp->waitlist[i + 1] = rdp->waitlist[i]; + rdp->waittail[i + 1] = rdp->waittail[i]; + wlc++; + } else { + rdp->waitlist[i + 1] = NULL; + rdp->waittail[i + 1] = + &rdp->waitlist[i + 1]; + } + } + if (rdp->nextlist != NULL) { + rdp->waitlist[0] = rdp->nextlist; + rdp->waittail[0] = rdp->nexttail; + wlc++; + rdp->nextlist = NULL; + rdp->nexttail = &rdp->nextlist; + RCU_TRACE_RDP(rcupreempt_trace_move2wait, rdp); + } else { + rdp->waitlist[0] = NULL; + rdp->waittail[0] = &rdp->waitlist[0]; + } + rdp->waitlistcount = wlc; + rdp->completed = rcu_ctrlblk.completed; + } + + /* + * Check to see if this CPU needs to report that it has seen + * the most recent counter flip, thereby declaring that all + * subsequent rcu_read_lock() invocations will respect this flip. + */ + + cpu = raw_smp_processor_id(); + if (per_cpu(rcu_flip_flag, cpu) == rcu_flipped) { + smp_mb(); /* Subsequent counter accesses must see new value */ + per_cpu(rcu_flip_flag, cpu) = rcu_flip_seen; + smp_mb(); /* Subsequent RCU read-side critical sections */ + /* seen -after- acknowledgement. */ + } +} + +DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_dyntick_sched, rcu_dyntick_sched) = { + .dynticks = 1, +}; + +#ifdef CONFIG_NO_HZ +static DEFINE_PER_CPU(int, rcu_update_flag); + +/** + * rcu_irq_enter - Called from Hard irq handlers and NMI/SMI. + * + * If the CPU was idle with dynamic ticks active, this updates the + * rcu_dyntick_sched.dynticks to let the RCU handling know that the + * CPU is active. + */ +void rcu_irq_enter(void) +{ + int cpu = smp_processor_id(); + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu); + + if (per_cpu(rcu_update_flag, cpu)) + per_cpu(rcu_update_flag, cpu)++; + + /* + * Only update if we are coming from a stopped ticks mode + * (rcu_dyntick_sched.dynticks is even). + */ + if (!in_interrupt() && + (rdssp->dynticks & 0x1) == 0) { + /* + * The following might seem like we could have a race + * with NMI/SMIs. But this really isn't a problem. + * Here we do a read/modify/write, and the race happens + * when an NMI/SMI comes in after the read and before + * the write. But NMI/SMIs will increment this counter + * twice before returning, so the zero bit will not + * be corrupted by the NMI/SMI which is the most important + * part. + * + * The only thing is that we would bring back the counter + * to a postion that it was in during the NMI/SMI. + * But the zero bit would be set, so the rest of the + * counter would again be ignored. + * + * On return from the IRQ, the counter may have the zero + * bit be 0 and the counter the same as the return from + * the NMI/SMI. If the state machine was so unlucky to + * see that, it still doesn't matter, since all + * RCU read-side critical sections on this CPU would + * have already completed. + */ + rdssp->dynticks++; + /* + * The following memory barrier ensures that any + * rcu_read_lock() primitives in the irq handler + * are seen by other CPUs to follow the above + * increment to rcu_dyntick_sched.dynticks. This is + * required in order for other CPUs to correctly + * determine when it is safe to advance the RCU + * grace-period state machine. + */ + smp_mb(); /* see above block comment. */ + /* + * Since we can't determine the dynamic tick mode from + * the rcu_dyntick_sched.dynticks after this routine, + * we use a second flag to acknowledge that we came + * from an idle state with ticks stopped. + */ + per_cpu(rcu_update_flag, cpu)++; + /* + * If we take an NMI/SMI now, they will also increment + * the rcu_update_flag, and will not update the + * rcu_dyntick_sched.dynticks on exit. That is for + * this IRQ to do. + */ + } +} + +/** + * rcu_irq_exit - Called from exiting Hard irq context. + * + * If the CPU was idle with dynamic ticks active, update the + * rcu_dyntick_sched.dynticks to put let the RCU handling be + * aware that the CPU is going back to idle with no ticks. + */ +void rcu_irq_exit(void) +{ + int cpu = smp_processor_id(); + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu); + + /* + * rcu_update_flag is set if we interrupted the CPU + * when it was idle with ticks stopped. + * Once this occurs, we keep track of interrupt nesting + * because a NMI/SMI could also come in, and we still + * only want the IRQ that started the increment of the + * rcu_dyntick_sched.dynticks to be the one that modifies + * it on exit. + */ + if (per_cpu(rcu_update_flag, cpu)) { + if (--per_cpu(rcu_update_flag, cpu)) + return; + + /* This must match the interrupt nesting */ + WARN_ON(in_interrupt()); + + /* + * If an NMI/SMI happens now we are still + * protected by the rcu_dyntick_sched.dynticks being odd. + */ + + /* + * The following memory barrier ensures that any + * rcu_read_unlock() primitives in the irq handler + * are seen by other CPUs to preceed the following + * increment to rcu_dyntick_sched.dynticks. This + * is required in order for other CPUs to determine + * when it is safe to advance the RCU grace-period + * state machine. + */ + smp_mb(); /* see above block comment. */ + rdssp->dynticks++; + WARN_ON(rdssp->dynticks & 0x1); + } +} + +static void dyntick_save_progress_counter(int cpu) +{ + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu); + + rdssp->dynticks_snap = rdssp->dynticks; +} + +static inline int +rcu_try_flip_waitack_needed(int cpu) +{ + long curr; + long snap; + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu); + + curr = rdssp->dynticks; + snap = rdssp->dynticks_snap; + smp_mb(); /* force ordering with cpu entering/leaving dynticks. */ + + /* + * If the CPU remained in dynticks mode for the entire time + * and didn't take any interrupts, NMIs, SMIs, or whatever, + * then it cannot be in the middle of an rcu_read_lock(), so + * the next rcu_read_lock() it executes must use the new value + * of the counter. So we can safely pretend that this CPU + * already acknowledged the counter. + */ + + if ((curr == snap) && ((curr & 0x1) == 0)) + return 0; + + /* + * If the CPU passed through or entered a dynticks idle phase with + * no active irq handlers, then, as above, we can safely pretend + * that this CPU already acknowledged the counter. + */ + + if ((curr - snap) > 2 || (curr & 0x1) == 0) + return 0; + + /* We need this CPU to explicitly acknowledge the counter flip. */ + + return 1; +} + +static inline int +rcu_try_flip_waitmb_needed(int cpu) +{ + long curr; + long snap; + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu); + + curr = rdssp->dynticks; + snap = rdssp->dynticks_snap; + smp_mb(); /* force ordering with cpu entering/leaving dynticks. */ + + /* + * If the CPU remained in dynticks mode for the entire time + * and didn't take any interrupts, NMIs, SMIs, or whatever, + * then it cannot have executed an RCU read-side critical section + * during that time, so there is no need for it to execute a + * memory barrier. + */ + + if ((curr == snap) && ((curr & 0x1) == 0)) + return 0; + + /* + * If the CPU either entered or exited an outermost interrupt, + * SMI, NMI, or whatever handler, then we know that it executed + * a memory barrier when doing so. So we don't need another one. + */ + if (curr != snap) + return 0; + + /* We need the CPU to execute a memory barrier. */ + + return 1; +} + +static void dyntick_save_progress_counter_sched(int cpu) +{ + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu); + + rdssp->sched_dynticks_snap = rdssp->dynticks; +} + +static int rcu_qsctr_inc_needed_dyntick(int cpu) +{ + long curr; + long snap; + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu); + + curr = rdssp->dynticks; + snap = rdssp->sched_dynticks_snap; + smp_mb(); /* force ordering with cpu entering/leaving dynticks. */ + + /* + * If the CPU remained in dynticks mode for the entire time + * and didn't take any interrupts, NMIs, SMIs, or whatever, + * then it cannot be in the middle of an rcu_read_lock(), so + * the next rcu_read_lock() it executes must use the new value + * of the counter. Therefore, this CPU has been in a quiescent + * state the entire time, and we don't need to wait for it. + */ + + if ((curr == snap) && ((curr & 0x1) == 0)) + return 0; + + /* + * If the CPU passed through or entered a dynticks idle phase with + * no active irq handlers, then, as above, this CPU has already + * passed through a quiescent state. + */ + + if ((curr - snap) > 2 || (snap & 0x1) == 0) + return 0; + + /* We need this CPU to go through a quiescent state. */ + + return 1; +} + +#else /* !CONFIG_NO_HZ */ + +# define dyntick_save_progress_counter(cpu) do { } while (0) +# define rcu_try_flip_waitack_needed(cpu) (1) +# define rcu_try_flip_waitmb_needed(cpu) (1) + +# define dyntick_save_progress_counter_sched(cpu) do { } while (0) +# define rcu_qsctr_inc_needed_dyntick(cpu) (1) + +#endif /* CONFIG_NO_HZ */ + +static void save_qsctr_sched(int cpu) +{ + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu); + + rdssp->sched_qs_snap = rdssp->sched_qs; +} + +static inline int rcu_qsctr_inc_needed(int cpu) +{ + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu); + + /* + * If there has been a quiescent state, no more need to wait + * on this CPU. + */ + + if (rdssp->sched_qs != rdssp->sched_qs_snap) { + smp_mb(); /* force ordering with cpu entering schedule(). */ + return 0; + } + + /* We need this CPU to go through a quiescent state. */ + + return 1; +} + +/* + * Get here when RCU is idle. Decide whether we need to + * move out of idle state, and return non-zero if so. + * "Straightforward" approach for the moment, might later + * use callback-list lengths, grace-period duration, or + * some such to determine when to exit idle state. + * Might also need a pre-idle test that does not acquire + * the lock, but let's get the simple case working first... + */ + +static int +rcu_try_flip_idle(void) +{ + int cpu; + + RCU_TRACE_ME(rcupreempt_trace_try_flip_i1); + if (!rcu_pending(smp_processor_id())) { + RCU_TRACE_ME(rcupreempt_trace_try_flip_ie1); + return 0; + } + + /* + * Do the flip. + */ + + RCU_TRACE_ME(rcupreempt_trace_try_flip_g1); + rcu_ctrlblk.completed++; /* stands in for rcu_try_flip_g2 */ + + /* + * Need a memory barrier so that other CPUs see the new + * counter value before they see the subsequent change of all + * the rcu_flip_flag instances to rcu_flipped. + */ + + smp_mb(); /* see above block comment. */ + + /* Now ask each CPU for acknowledgement of the flip. */ + + for_each_cpu_mask_nr(cpu, rcu_cpu_online_map) { + per_cpu(rcu_flip_flag, cpu) = rcu_flipped; + dyntick_save_progress_counter(cpu); + } + + return 1; +} + +/* + * Wait for CPUs to acknowledge the flip. + */ + +static int +rcu_try_flip_waitack(void) +{ + int cpu; + + RCU_TRACE_ME(rcupreempt_trace_try_flip_a1); + for_each_cpu_mask_nr(cpu, rcu_cpu_online_map) + if (rcu_try_flip_waitack_needed(cpu) && + per_cpu(rcu_flip_flag, cpu) != rcu_flip_seen) { + RCU_TRACE_ME(rcupreempt_trace_try_flip_ae1); + return 0; + } + + /* + * Make sure our checks above don't bleed into subsequent + * waiting for the sum of the counters to reach zero. + */ + + smp_mb(); /* see above block comment. */ + RCU_TRACE_ME(rcupreempt_trace_try_flip_a2); + return 1; +} + +/* + * Wait for collective ``last'' counter to reach zero, + * then tell all CPUs to do an end-of-grace-period memory barrier. + */ + +static int +rcu_try_flip_waitzero(void) +{ + int cpu; + int lastidx = !(rcu_ctrlblk.completed & 0x1); + int sum = 0; + + /* Check to see if the sum of the "last" counters is zero. */ + + RCU_TRACE_ME(rcupreempt_trace_try_flip_z1); + for_each_cpu_mask_nr(cpu, rcu_cpu_online_map) + sum += RCU_DATA_CPU(cpu)->rcu_flipctr[lastidx]; + if (sum != 0) { + RCU_TRACE_ME(rcupreempt_trace_try_flip_ze1); + return 0; + } + + /* + * This ensures that the other CPUs see the call for + * memory barriers -after- the sum to zero has been + * detected here + */ + smp_mb(); /* ^^^^^^^^^^^^ */ + + /* Call for a memory barrier from each CPU. */ + for_each_cpu_mask_nr(cpu, rcu_cpu_online_map) { + per_cpu(rcu_mb_flag, cpu) = rcu_mb_needed; + dyntick_save_progress_counter(cpu); + } + + RCU_TRACE_ME(rcupreempt_trace_try_flip_z2); + return 1; +} + +/* + * Wait for all CPUs to do their end-of-grace-period memory barrier. + * Return 0 once all CPUs have done so. + */ + +static int +rcu_try_flip_waitmb(void) +{ + int cpu; + + RCU_TRACE_ME(rcupreempt_trace_try_flip_m1); + for_each_cpu_mask_nr(cpu, rcu_cpu_online_map) + if (rcu_try_flip_waitmb_needed(cpu) && + per_cpu(rcu_mb_flag, cpu) != rcu_mb_done) { + RCU_TRACE_ME(rcupreempt_trace_try_flip_me1); + return 0; + } + + smp_mb(); /* Ensure that the above checks precede any following flip. */ + RCU_TRACE_ME(rcupreempt_trace_try_flip_m2); + return 1; +} + +/* + * Attempt a single flip of the counters. Remember, a single flip does + * -not- constitute a grace period. Instead, the interval between + * at least GP_STAGES consecutive flips is a grace period. + * + * If anyone is nuts enough to run this CONFIG_PREEMPT_RCU implementation + * on a large SMP, they might want to use a hierarchical organization of + * the per-CPU-counter pairs. + */ +static void rcu_try_flip(void) +{ + unsigned long flags; + + RCU_TRACE_ME(rcupreempt_trace_try_flip_1); + if (unlikely(!spin_trylock_irqsave(&rcu_ctrlblk.fliplock, flags))) { + RCU_TRACE_ME(rcupreempt_trace_try_flip_e1); + return; + } + + /* + * Take the next transition(s) through the RCU grace-period + * flip-counter state machine. + */ + + switch (rcu_ctrlblk.rcu_try_flip_state) { + case rcu_try_flip_idle_state: + if (rcu_try_flip_idle()) + rcu_ctrlblk.rcu_try_flip_state = + rcu_try_flip_waitack_state; + break; + case rcu_try_flip_waitack_state: + if (rcu_try_flip_waitack()) + rcu_ctrlblk.rcu_try_flip_state = + rcu_try_flip_waitzero_state; + break; + case rcu_try_flip_waitzero_state: + if (rcu_try_flip_waitzero()) + rcu_ctrlblk.rcu_try_flip_state = + rcu_try_flip_waitmb_state; + break; + case rcu_try_flip_waitmb_state: + if (rcu_try_flip_waitmb()) + rcu_ctrlblk.rcu_try_flip_state = + rcu_try_flip_idle_state; + } + spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags); +} + +/* + * Check to see if this CPU needs to do a memory barrier in order to + * ensure that any prior RCU read-side critical sections have committed + * their counter manipulations and critical-section memory references + * before declaring the grace period to be completed. + */ +static void rcu_check_mb(int cpu) +{ + if (per_cpu(rcu_mb_flag, cpu) == rcu_mb_needed) { + smp_mb(); /* Ensure RCU read-side accesses are visible. */ + per_cpu(rcu_mb_flag, cpu) = rcu_mb_done; + } +} + +void rcu_check_callbacks(int cpu, int user) +{ + unsigned long flags; + struct rcu_data *rdp = RCU_DATA_CPU(cpu); + + /* + * If this CPU took its interrupt from user mode or from the + * idle loop, and this is not a nested interrupt, then + * this CPU has to have exited all prior preept-disable + * sections of code. So increment the counter to note this. + * + * The memory barrier is needed to handle the case where + * writes from a preempt-disable section of code get reordered + * into schedule() by this CPU's write buffer. So the memory + * barrier makes sure that the rcu_qsctr_inc() is seen by other + * CPUs to happen after any such write. + */ + + if (user || + (idle_cpu(cpu) && !in_softirq() && + hardirq_count() <= (1 << HARDIRQ_SHIFT))) { + smp_mb(); /* Guard against aggressive schedule(). */ + rcu_qsctr_inc(cpu); + } + + rcu_check_mb(cpu); + if (rcu_ctrlblk.completed == rdp->completed) + rcu_try_flip(); + spin_lock_irqsave(&rdp->lock, flags); + RCU_TRACE_RDP(rcupreempt_trace_check_callbacks, rdp); + __rcu_advance_callbacks(rdp); + if (rdp->donelist == NULL) { + spin_unlock_irqrestore(&rdp->lock, flags); + } else { + spin_unlock_irqrestore(&rdp->lock, flags); + raise_softirq(RCU_SOFTIRQ); + } +} + +/* + * Needed by dynticks, to make sure all RCU processing has finished + * when we go idle: + */ +void rcu_advance_callbacks(int cpu, int user) +{ + unsigned long flags; + struct rcu_data *rdp = RCU_DATA_CPU(cpu); + + if (rcu_ctrlblk.completed == rdp->completed) { + rcu_try_flip(); + if (rcu_ctrlblk.completed == rdp->completed) + return; + } + spin_lock_irqsave(&rdp->lock, flags); + RCU_TRACE_RDP(rcupreempt_trace_check_callbacks, rdp); + __rcu_advance_callbacks(rdp); + spin_unlock_irqrestore(&rdp->lock, flags); +} + +#ifdef CONFIG_HOTPLUG_CPU +#define rcu_offline_cpu_enqueue(srclist, srctail, dstlist, dsttail) do { \ + *dsttail = srclist; \ + if (srclist != NULL) { \ + dsttail = srctail; \ + srclist = NULL; \ + srctail = &srclist;\ + } \ + } while (0) + +void rcu_offline_cpu(int cpu) +{ + int i; + struct rcu_head *list = NULL; + unsigned long flags; + struct rcu_data *rdp = RCU_DATA_CPU(cpu); + struct rcu_head *schedlist = NULL; + struct rcu_head **schedtail = &schedlist; + struct rcu_head **tail = &list; + + /* + * Remove all callbacks from the newly dead CPU, retaining order. + * Otherwise rcu_barrier() will fail + */ + + spin_lock_irqsave(&rdp->lock, flags); + rcu_offline_cpu_enqueue(rdp->donelist, rdp->donetail, list, tail); + for (i = GP_STAGES - 1; i >= 0; i--) + rcu_offline_cpu_enqueue(rdp->waitlist[i], rdp->waittail[i], + list, tail); + rcu_offline_cpu_enqueue(rdp->nextlist, rdp->nexttail, list, tail); + rcu_offline_cpu_enqueue(rdp->waitschedlist, rdp->waitschedtail, + schedlist, schedtail); + rcu_offline_cpu_enqueue(rdp->nextschedlist, rdp->nextschedtail, + schedlist, schedtail); + rdp->rcu_sched_sleeping = 0; + spin_unlock_irqrestore(&rdp->lock, flags); + rdp->waitlistcount = 0; + + /* Disengage the newly dead CPU from the grace-period computation. */ + + spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags); + rcu_check_mb(cpu); + if (per_cpu(rcu_flip_flag, cpu) == rcu_flipped) { + smp_mb(); /* Subsequent counter accesses must see new value */ + per_cpu(rcu_flip_flag, cpu) = rcu_flip_seen; + smp_mb(); /* Subsequent RCU read-side critical sections */ + /* seen -after- acknowledgement. */ + } + + RCU_DATA_ME()->rcu_flipctr[0] += RCU_DATA_CPU(cpu)->rcu_flipctr[0]; + RCU_DATA_ME()->rcu_flipctr[1] += RCU_DATA_CPU(cpu)->rcu_flipctr[1]; + + RCU_DATA_CPU(cpu)->rcu_flipctr[0] = 0; + RCU_DATA_CPU(cpu)->rcu_flipctr[1] = 0; + + cpu_clear(cpu, rcu_cpu_online_map); + + spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags); + + /* + * Place the removed callbacks on the current CPU's queue. + * Make them all start a new grace period: simple approach, + * in theory could starve a given set of callbacks, but + * you would need to be doing some serious CPU hotplugging + * to make this happen. If this becomes a problem, adding + * a synchronize_rcu() to the hotplug path would be a simple + * fix. + */ + + local_irq_save(flags); /* disable preempt till we know what lock. */ + rdp = RCU_DATA_ME(); + spin_lock(&rdp->lock); + *rdp->nexttail = list; + if (list) + rdp->nexttail = tail; + *rdp->nextschedtail = schedlist; + if (schedlist) + rdp->nextschedtail = schedtail; + spin_unlock_irqrestore(&rdp->lock, flags); +} + +#else /* #ifdef CONFIG_HOTPLUG_CPU */ + +void rcu_offline_cpu(int cpu) +{ +} + +#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */ + +void __cpuinit rcu_online_cpu(int cpu) +{ + unsigned long flags; + struct rcu_data *rdp; + + spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags); + cpu_set(cpu, rcu_cpu_online_map); + spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags); + + /* + * The rcu_sched grace-period processing might have bypassed + * this CPU, given that it was not in the rcu_cpu_online_map + * when the grace-period scan started. This means that the + * grace-period task might sleep. So make sure that if this + * should happen, the first callback posted to this CPU will + * wake up the grace-period task if need be. + */ + + rdp = RCU_DATA_CPU(cpu); + spin_lock_irqsave(&rdp->lock, flags); + rdp->rcu_sched_sleeping = 1; + spin_unlock_irqrestore(&rdp->lock, flags); +} + +static void rcu_process_callbacks(struct softirq_action *unused) +{ + unsigned long flags; + struct rcu_head *next, *list; + struct rcu_data *rdp; + + local_irq_save(flags); + rdp = RCU_DATA_ME(); + spin_lock(&rdp->lock); + list = rdp->donelist; + if (list == NULL) { + spin_unlock_irqrestore(&rdp->lock, flags); + return; + } + rdp->donelist = NULL; + rdp->donetail = &rdp->donelist; + RCU_TRACE_RDP(rcupreempt_trace_done_remove, rdp); + spin_unlock_irqrestore(&rdp->lock, flags); + while (list) { + next = list->next; + list->func(list); + list = next; + RCU_TRACE_ME(rcupreempt_trace_invoke); + } +} + +void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) +{ + unsigned long flags; + struct rcu_data *rdp; + + head->func = func; + head->next = NULL; + local_irq_save(flags); + rdp = RCU_DATA_ME(); + spin_lock(&rdp->lock); + __rcu_advance_callbacks(rdp); + *rdp->nexttail = head; + rdp->nexttail = &head->next; + RCU_TRACE_RDP(rcupreempt_trace_next_add, rdp); + spin_unlock_irqrestore(&rdp->lock, flags); +} +EXPORT_SYMBOL_GPL(call_rcu); + +void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) +{ + unsigned long flags; + struct rcu_data *rdp; + int wake_gp = 0; + + head->func = func; + head->next = NULL; + local_irq_save(flags); + rdp = RCU_DATA_ME(); + spin_lock(&rdp->lock); + *rdp->nextschedtail = head; + rdp->nextschedtail = &head->next; + if (rdp->rcu_sched_sleeping) { + + /* Grace-period processing might be sleeping... */ + + rdp->rcu_sched_sleeping = 0; + wake_gp = 1; + } + spin_unlock_irqrestore(&rdp->lock, flags); + if (wake_gp) { + + /* Wake up grace-period processing, unless someone beat us. */ + + spin_lock_irqsave(&rcu_ctrlblk.schedlock, flags); + if (rcu_ctrlblk.sched_sleep != rcu_sched_sleeping) + wake_gp = 0; + rcu_ctrlblk.sched_sleep = rcu_sched_not_sleeping; + spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags); + if (wake_gp) + wake_up_interruptible(&rcu_ctrlblk.sched_wq); + } +} +EXPORT_SYMBOL_GPL(call_rcu_sched); + +/* + * Wait until all currently running preempt_disable() code segments + * (including hardware-irq-disable segments) complete. Note that + * in -rt this does -not- necessarily result in all currently executing + * interrupt -handlers- having completed. + */ +synchronize_rcu_xxx(__synchronize_sched, call_rcu_sched) +EXPORT_SYMBOL_GPL(__synchronize_sched); + +/* + * kthread function that manages call_rcu_sched grace periods. + */ +static int rcu_sched_grace_period(void *arg) +{ + int couldsleep; /* might sleep after current pass. */ + int couldsleepnext = 0; /* might sleep after next pass. */ + int cpu; + unsigned long flags; + struct rcu_data *rdp; + int ret; + + /* + * Each pass through the following loop handles one + * rcu_sched grace period cycle. + */ + do { + /* Save each CPU's current state. */ + + for_each_online_cpu(cpu) { + dyntick_save_progress_counter_sched(cpu); + save_qsctr_sched(cpu); + } + + /* + * Sleep for about an RCU grace-period's worth to + * allow better batching and to consume less CPU. + */ + schedule_timeout_interruptible(RCU_SCHED_BATCH_TIME); + + /* + * If there was nothing to do last time, prepare to + * sleep at the end of the current grace period cycle. + */ + couldsleep = couldsleepnext; + couldsleepnext = 1; + if (couldsleep) { + spin_lock_irqsave(&rcu_ctrlblk.schedlock, flags); + rcu_ctrlblk.sched_sleep = rcu_sched_sleep_prep; + spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags); + } + + /* + * Wait on each CPU in turn to have either visited + * a quiescent state or been in dynticks-idle mode. + */ + for_each_online_cpu(cpu) { + while (rcu_qsctr_inc_needed(cpu) && + rcu_qsctr_inc_needed_dyntick(cpu)) { + /* resched_cpu(cpu); @@@ */ + schedule_timeout_interruptible(1); + } + } + + /* Advance callbacks for each CPU. */ + + for_each_online_cpu(cpu) { + + rdp = RCU_DATA_CPU(cpu); + spin_lock_irqsave(&rdp->lock, flags); + + /* + * We are running on this CPU irq-disabled, so no + * CPU can go offline until we re-enable irqs. + * The current CPU might have already gone + * offline (between the for_each_offline_cpu and + * the spin_lock_irqsave), but in that case all its + * callback lists will be empty, so no harm done. + * + * Advance the callbacks! We share normal RCU's + * donelist, since callbacks are invoked the + * same way in either case. + */ + if (rdp->waitschedlist != NULL) { + *rdp->donetail = rdp->waitschedlist; + rdp->donetail = rdp->waitschedtail; + + /* + * Next rcu_check_callbacks() will + * do the required raise_softirq(). + */ + } + if (rdp->nextschedlist != NULL) { + rdp->waitschedlist = rdp->nextschedlist; + rdp->waitschedtail = rdp->nextschedtail; + couldsleep = 0; + couldsleepnext = 0; + } else { + rdp->waitschedlist = NULL; + rdp->waitschedtail = &rdp->waitschedlist; + } + rdp->nextschedlist = NULL; + rdp->nextschedtail = &rdp->nextschedlist; + + /* Mark sleep intention. */ + + rdp->rcu_sched_sleeping = couldsleep; + + spin_unlock_irqrestore(&rdp->lock, flags); + } + + /* If we saw callbacks on the last scan, go deal with them. */ + + if (!couldsleep) + continue; + + /* Attempt to block... */ + + spin_lock_irqsave(&rcu_ctrlblk.schedlock, flags); + if (rcu_ctrlblk.sched_sleep != rcu_sched_sleep_prep) { + + /* + * Someone posted a callback after we scanned. + * Go take care of it. + */ + spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags); + couldsleepnext = 0; + continue; + } + + /* Block until the next person posts a callback. */ + + rcu_ctrlblk.sched_sleep = rcu_sched_sleeping; + spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags); + ret = 0; + __wait_event_interruptible(rcu_ctrlblk.sched_wq, + rcu_ctrlblk.sched_sleep != rcu_sched_sleeping, + ret); + + /* + * Signals would prevent us from sleeping, and we cannot + * do much with them in any case. So flush them. + */ + if (ret) + flush_signals(current); + couldsleepnext = 0; + + } while (!kthread_should_stop()); + + return (0); +} + +/* + * Check to see if any future RCU-related work will need to be done + * by the current CPU, even if none need be done immediately, returning + * 1 if so. Assumes that notifiers would take care of handling any + * outstanding requests from the RCU core. + * + * This function is part of the RCU implementation; it is -not- + * an exported member of the RCU API. + */ +int rcu_needs_cpu(int cpu) +{ + struct rcu_data *rdp = RCU_DATA_CPU(cpu); + + return (rdp->donelist != NULL || + !!rdp->waitlistcount || + rdp->nextlist != NULL || + rdp->nextschedlist != NULL || + rdp->waitschedlist != NULL); +} + +int rcu_pending(int cpu) +{ + struct rcu_data *rdp = RCU_DATA_CPU(cpu); + + /* The CPU has at least one callback queued somewhere. */ + + if (rdp->donelist != NULL || + !!rdp->waitlistcount || + rdp->nextlist != NULL || + rdp->nextschedlist != NULL || + rdp->waitschedlist != NULL) + return 1; + + /* The RCU core needs an acknowledgement from this CPU. */ + + if ((per_cpu(rcu_flip_flag, cpu) == rcu_flipped) || + (per_cpu(rcu_mb_flag, cpu) == rcu_mb_needed)) + return 1; + + /* This CPU has fallen behind the global grace-period number. */ + + if (rdp->completed != rcu_ctrlblk.completed) + return 1; + + /* Nothing needed from this CPU. */ + + return 0; +} + +static int __cpuinit rcu_cpu_notify(struct notifier_block *self, + unsigned long action, void *hcpu) +{ + long cpu = (long)hcpu; + + switch (action) { + case CPU_UP_PREPARE: + case CPU_UP_PREPARE_FROZEN: + rcu_online_cpu(cpu); + break; + case CPU_UP_CANCELED: + case CPU_UP_CANCELED_FROZEN: + case CPU_DEAD: + case CPU_DEAD_FROZEN: + rcu_offline_cpu(cpu); + break; + default: + break; + } + return NOTIFY_OK; +} + +static struct notifier_block __cpuinitdata rcu_nb = { + .notifier_call = rcu_cpu_notify, +}; + +void __init __rcu_init(void) +{ + int cpu; + int i; + struct rcu_data *rdp; + + printk(KERN_NOTICE "Preemptible RCU implementation.\n"); + for_each_possible_cpu(cpu) { + rdp = RCU_DATA_CPU(cpu); + spin_lock_init(&rdp->lock); + rdp->completed = 0; + rdp->waitlistcount = 0; + rdp->nextlist = NULL; + rdp->nexttail = &rdp->nextlist; + for (i = 0; i < GP_STAGES; i++) { + rdp->waitlist[i] = NULL; + rdp->waittail[i] = &rdp->waitlist[i]; + } + rdp->donelist = NULL; + rdp->donetail = &rdp->donelist; + rdp->rcu_flipctr[0] = 0; + rdp->rcu_flipctr[1] = 0; + rdp->nextschedlist = NULL; + rdp->nextschedtail = &rdp->nextschedlist; + rdp->waitschedlist = NULL; + rdp->waitschedtail = &rdp->waitschedlist; + rdp->rcu_sched_sleeping = 0; + } + register_cpu_notifier(&rcu_nb); + + /* + * We don't need protection against CPU-Hotplug here + * since + * a) If a CPU comes online while we are iterating over the + * cpu_online_map below, we would only end up making a + * duplicate call to rcu_online_cpu() which sets the corresponding + * CPU's mask in the rcu_cpu_online_map. + * + * b) A CPU cannot go offline at this point in time since the user + * does not have access to the sysfs interface, nor do we + * suspend the system. + */ + for_each_online_cpu(cpu) + rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long) cpu); + + open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); +} + +/* + * Late-boot-time RCU initialization that must wait until after scheduler + * has been initialized. + */ +void __init rcu_init_sched(void) +{ + rcu_sched_grace_period_task = kthread_run(rcu_sched_grace_period, + NULL, + "rcu_sched_grace_period"); + WARN_ON(IS_ERR(rcu_sched_grace_period_task)); +} + +#ifdef CONFIG_RCU_TRACE +long *rcupreempt_flipctr(int cpu) +{ + return &RCU_DATA_CPU(cpu)->rcu_flipctr[0]; +} +EXPORT_SYMBOL_GPL(rcupreempt_flipctr); + +int rcupreempt_flip_flag(int cpu) +{ + return per_cpu(rcu_flip_flag, cpu); +} +EXPORT_SYMBOL_GPL(rcupreempt_flip_flag); + +int rcupreempt_mb_flag(int cpu) +{ + return per_cpu(rcu_mb_flag, cpu); +} +EXPORT_SYMBOL_GPL(rcupreempt_mb_flag); + +char *rcupreempt_try_flip_state_name(void) +{ + return rcu_try_flip_state_names[rcu_ctrlblk.rcu_try_flip_state]; +} +EXPORT_SYMBOL_GPL(rcupreempt_try_flip_state_name); + +struct rcupreempt_trace *rcupreempt_trace_cpu(int cpu) +{ + struct rcu_data *rdp = RCU_DATA_CPU(cpu); + + return &rdp->trace; +} +EXPORT_SYMBOL_GPL(rcupreempt_trace_cpu); + +#endif /* #ifdef RCU_TRACE */ |
