diff options
Diffstat (limited to 'kernel/rcupdate.c')
| -rw-r--r-- | kernel/rcupdate.c | 470 |
1 files changed, 470 insertions, 0 deletions
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c new file mode 100644 index 0000000..d00eded --- /dev/null +++ b/kernel/rcupdate.c @@ -0,0 +1,470 @@ +/* + * 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, write to the Free Software + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * + * Copyright (C) IBM Corporation, 2001 + * + * Authors: Dipankar Sarma <dipankar@in.ibm.com> + * Manfred Spraul <manfred@colorfullife.com> + * + * Based on the original work by Paul McKenney <paulmck@us.ibm.com> + * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. + * Papers: + * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf + * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) + * + * For detailed explanation of Read-Copy Update mechanism see - + * http://lse.sourceforge.net/locking/rcupdate.html + * + */ +#include <linux/types.h> +#include <linux/kernel.h> +#include <linux/init.h> +#include <linux/spinlock.h> +#include <linux/smp.h> +#include <linux/interrupt.h> +#include <linux/sched.h> +#include <asm/atomic.h> +#include <linux/bitops.h> +#include <linux/module.h> +#include <linux/completion.h> +#include <linux/moduleparam.h> +#include <linux/percpu.h> +#include <linux/notifier.h> +#include <linux/rcupdate.h> +#include <linux/cpu.h> + +/* Definition for rcupdate control block. */ +struct rcu_ctrlblk rcu_ctrlblk = + { .cur = -300, .completed = -300 }; +struct rcu_ctrlblk rcu_bh_ctrlblk = + { .cur = -300, .completed = -300 }; + +/* Bookkeeping of the progress of the grace period */ +struct rcu_state { + spinlock_t lock; /* Guard this struct and writes to rcu_ctrlblk */ + cpumask_t cpumask; /* CPUs that need to switch in order */ + /* for current batch to proceed. */ +}; + +static struct rcu_state rcu_state ____cacheline_maxaligned_in_smp = + {.lock = SPIN_LOCK_UNLOCKED, .cpumask = CPU_MASK_NONE }; +static struct rcu_state rcu_bh_state ____cacheline_maxaligned_in_smp = + {.lock = SPIN_LOCK_UNLOCKED, .cpumask = CPU_MASK_NONE }; + +DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L }; +DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L }; + +/* Fake initialization required by compiler */ +static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL}; +static int maxbatch = 10; + +/** + * call_rcu - Queue an RCU callback for invocation after a grace period. + * @head: structure to be used for queueing the RCU updates. + * @func: actual update function to be invoked after the grace period + * + * The update function will be invoked some time after a full grace + * period elapses, in other words after all currently executing RCU + * read-side critical sections have completed. RCU read-side critical + * sections are delimited by rcu_read_lock() and rcu_read_unlock(), + * and may be nested. + */ +void fastcall 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 = &__get_cpu_var(rcu_data); + *rdp->nxttail = head; + rdp->nxttail = &head->next; + local_irq_restore(flags); +} + +/** + * call_rcu_bh - Queue an RCU for invocation after a quicker grace period. + * @head: structure to be used for queueing the RCU updates. + * @func: actual update function to be invoked after the grace period + * + * The update function will be invoked some time after a full grace + * period elapses, in other words after all currently executing RCU + * read-side critical sections have completed. call_rcu_bh() assumes + * that the read-side critical sections end on completion of a softirq + * handler. This means that read-side critical sections in process + * context must not be interrupted by softirqs. This interface is to be + * used when most of the read-side critical sections are in softirq context. + * RCU read-side critical sections are delimited by rcu_read_lock() and + * rcu_read_unlock(), * if in interrupt context or rcu_read_lock_bh() + * and rcu_read_unlock_bh(), if in process context. These may be nested. + */ +void fastcall call_rcu_bh(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 = &__get_cpu_var(rcu_bh_data); + *rdp->nxttail = head; + rdp->nxttail = &head->next; + local_irq_restore(flags); +} + +/* + * Invoke the completed RCU callbacks. They are expected to be in + * a per-cpu list. + */ +static void rcu_do_batch(struct rcu_data *rdp) +{ + struct rcu_head *next, *list; + int count = 0; + + list = rdp->donelist; + while (list) { + next = rdp->donelist = list->next; + list->func(list); + list = next; + if (++count >= maxbatch) + break; + } + if (!rdp->donelist) + rdp->donetail = &rdp->donelist; + else + tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu)); +} + +/* + * Grace period handling: + * The grace period handling consists out of two steps: + * - A new grace period is started. + * This is done by rcu_start_batch. The start is not broadcasted to + * all cpus, they must pick this up by comparing rcp->cur with + * rdp->quiescbatch. All cpus are recorded in the + * rcu_state.cpumask bitmap. + * - All cpus must go through a quiescent state. + * Since the start of the grace period is not broadcasted, at least two + * calls to rcu_check_quiescent_state are required: + * The first call just notices that a new grace period is running. The + * following calls check if there was a quiescent state since the beginning + * of the grace period. If so, it updates rcu_state.cpumask. If + * the bitmap is empty, then the grace period is completed. + * rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace + * period (if necessary). + */ +/* + * Register a new batch of callbacks, and start it up if there is currently no + * active batch and the batch to be registered has not already occurred. + * Caller must hold rcu_state.lock. + */ +static void rcu_start_batch(struct rcu_ctrlblk *rcp, struct rcu_state *rsp, + int next_pending) +{ + if (next_pending) + rcp->next_pending = 1; + + if (rcp->next_pending && + rcp->completed == rcp->cur) { + /* Can't change, since spin lock held. */ + cpus_andnot(rsp->cpumask, cpu_online_map, nohz_cpu_mask); + + rcp->next_pending = 0; + /* next_pending == 0 must be visible in __rcu_process_callbacks() + * before it can see new value of cur. + */ + smp_wmb(); + rcp->cur++; + } +} + +/* + * cpu went through a quiescent state since the beginning of the grace period. + * Clear it from the cpu mask and complete the grace period if it was the last + * cpu. Start another grace period if someone has further entries pending + */ +static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp, struct rcu_state *rsp) +{ + cpu_clear(cpu, rsp->cpumask); + if (cpus_empty(rsp->cpumask)) { + /* batch completed ! */ + rcp->completed = rcp->cur; + rcu_start_batch(rcp, rsp, 0); + } +} + +/* + * Check if the cpu has gone through a quiescent state (say context + * switch). If so and if it already hasn't done so in this RCU + * quiescent cycle, then indicate that it has done so. + */ +static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp, + struct rcu_state *rsp, struct rcu_data *rdp) +{ + if (rdp->quiescbatch != rcp->cur) { + /* start new grace period: */ + rdp->qs_pending = 1; + rdp->passed_quiesc = 0; + rdp->quiescbatch = rcp->cur; + return; + } + + /* Grace period already completed for this cpu? + * qs_pending is checked instead of the actual bitmap to avoid + * cacheline trashing. + */ + if (!rdp->qs_pending) + 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->passed_quiesc) + return; + rdp->qs_pending = 0; + + spin_lock(&rsp->lock); + /* + * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync + * during cpu startup. Ignore the quiescent state. + */ + if (likely(rdp->quiescbatch == rcp->cur)) + cpu_quiet(rdp->cpu, rcp, rsp); + + spin_unlock(&rsp->lock); +} + + +#ifdef CONFIG_HOTPLUG_CPU + +/* warning! helper for rcu_offline_cpu. do not use elsewhere without reviewing + * locking requirements, the list it's pulling from has to belong to a cpu + * which is dead and hence not processing interrupts. + */ +static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list, + struct rcu_head **tail) +{ + local_irq_disable(); + *this_rdp->nxttail = list; + if (list) + this_rdp->nxttail = tail; + local_irq_enable(); +} + +static void __rcu_offline_cpu(struct rcu_data *this_rdp, + struct rcu_ctrlblk *rcp, struct rcu_state *rsp, struct rcu_data *rdp) +{ + /* if the cpu going offline owns the grace period + * we can block indefinitely waiting for it, so flush + * it here + */ + spin_lock_bh(&rsp->lock); + if (rcp->cur != rcp->completed) + cpu_quiet(rdp->cpu, rcp, rsp); + spin_unlock_bh(&rsp->lock); + rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail); + rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail); + +} +static void rcu_offline_cpu(int cpu) +{ + struct rcu_data *this_rdp = &get_cpu_var(rcu_data); + struct rcu_data *this_bh_rdp = &get_cpu_var(rcu_bh_data); + + __rcu_offline_cpu(this_rdp, &rcu_ctrlblk, &rcu_state, + &per_cpu(rcu_data, cpu)); + __rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk, &rcu_bh_state, + &per_cpu(rcu_bh_data, cpu)); + put_cpu_var(rcu_data); + put_cpu_var(rcu_bh_data); + tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu); +} + +#else + +static void rcu_offline_cpu(int cpu) +{ +} + +#endif + +/* + * This does the RCU processing work from tasklet context. + */ +static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp, + struct rcu_state *rsp, struct rcu_data *rdp) +{ + if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) { + *rdp->donetail = rdp->curlist; + rdp->donetail = rdp->curtail; + rdp->curlist = NULL; + rdp->curtail = &rdp->curlist; + } + + local_irq_disable(); + if (rdp->nxtlist && !rdp->curlist) { + rdp->curlist = rdp->nxtlist; + rdp->curtail = rdp->nxttail; + rdp->nxtlist = NULL; + rdp->nxttail = &rdp->nxtlist; + local_irq_enable(); + + /* + * start the next batch of callbacks + */ + + /* determine batch number */ + rdp->batch = rcp->cur + 1; + /* see the comment and corresponding wmb() in + * the rcu_start_batch() + */ + smp_rmb(); + + if (!rcp->next_pending) { + /* and start it/schedule start if it's a new batch */ + spin_lock(&rsp->lock); + rcu_start_batch(rcp, rsp, 1); + spin_unlock(&rsp->lock); + } + } else { + local_irq_enable(); + } + rcu_check_quiescent_state(rcp, rsp, rdp); + if (rdp->donelist) + rcu_do_batch(rdp); +} + +static void rcu_process_callbacks(unsigned long unused) +{ + __rcu_process_callbacks(&rcu_ctrlblk, &rcu_state, + &__get_cpu_var(rcu_data)); + __rcu_process_callbacks(&rcu_bh_ctrlblk, &rcu_bh_state, + &__get_cpu_var(rcu_bh_data)); +} + +void rcu_check_callbacks(int cpu, int user) +{ + if (user || + (idle_cpu(cpu) && !in_softirq() && + hardirq_count() <= (1 << HARDIRQ_SHIFT))) { + rcu_qsctr_inc(cpu); + rcu_bh_qsctr_inc(cpu); + } else if (!in_softirq()) + rcu_bh_qsctr_inc(cpu); + tasklet_schedule(&per_cpu(rcu_tasklet, cpu)); +} + +static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp, + struct rcu_data *rdp) +{ + memset(rdp, 0, sizeof(*rdp)); + rdp->curtail = &rdp->curlist; + rdp->nxttail = &rdp->nxtlist; + rdp->donetail = &rdp->donelist; + rdp->quiescbatch = rcp->completed; + rdp->qs_pending = 0; + rdp->cpu = cpu; +} + +static void __devinit rcu_online_cpu(int cpu) +{ + struct rcu_data *rdp = &per_cpu(rcu_data, cpu); + struct rcu_data *bh_rdp = &per_cpu(rcu_bh_data, cpu); + + rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp); + rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp); + tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL); +} + +static int __devinit rcu_cpu_notify(struct notifier_block *self, + unsigned long action, void *hcpu) +{ + long cpu = (long)hcpu; + switch (action) { + case CPU_UP_PREPARE: + rcu_online_cpu(cpu); + break; + case CPU_DEAD: + rcu_offline_cpu(cpu); + break; + default: + break; + } + return NOTIFY_OK; +} + +static struct notifier_block __devinitdata rcu_nb = { + .notifier_call = rcu_cpu_notify, +}; + +/* + * Initializes rcu mechanism. Assumed to be called early. + * That is before local timer(SMP) or jiffie timer (uniproc) is setup. + * Note that rcu_qsctr and friends are implicitly + * initialized due to the choice of ``0'' for RCU_CTR_INVALID. + */ +void __init rcu_init(void) +{ + rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, + (void *)(long)smp_processor_id()); + /* Register notifier for non-boot CPUs */ + register_cpu_notifier(&rcu_nb); +} + +struct rcu_synchronize { + struct rcu_head head; + struct completion completion; +}; + +/* Because of FASTCALL declaration of complete, we use this wrapper */ +static void wakeme_after_rcu(struct rcu_head *head) +{ + struct rcu_synchronize *rcu; + + rcu = container_of(head, struct rcu_synchronize, head); + complete(&rcu->completion); +} + +/** + * synchronize_kernel - wait until a grace period has elapsed. + * + * Control will return to the caller some time after a full grace + * period has elapsed, in other words after all currently executing RCU + * read-side critical sections have completed. RCU read-side critical + * sections are delimited by rcu_read_lock() and rcu_read_unlock(), + * and may be nested. + */ +void synchronize_kernel(void) +{ + struct rcu_synchronize rcu; + + init_completion(&rcu.completion); + /* Will wake me after RCU finished */ + call_rcu(&rcu.head, wakeme_after_rcu); + + /* Wait for it */ + wait_for_completion(&rcu.completion); +} + +module_param(maxbatch, int, 0); +EXPORT_SYMBOL_GPL(call_rcu); +EXPORT_SYMBOL_GPL(call_rcu_bh); +EXPORT_SYMBOL_GPL(synchronize_kernel); |
