diff options
| -rw-r--r-- | Documentation/RCU/checklist.txt | 2 | ||||
| -rw-r--r-- | Documentation/RCU/rcuref.txt | 16 | ||||
| -rw-r--r-- | Documentation/RCU/whatisRCU.txt | 2 | ||||
| -rw-r--r-- | include/linux/compiler.h | 4 | ||||
| -rw-r--r-- | include/linux/rcuclassic.h | 37 | ||||
| -rw-r--r-- | include/linux/rculist.h | 14 | ||||
| -rw-r--r-- | include/linux/rcupdate.h | 20 | ||||
| -rw-r--r-- | include/linux/rcupreempt.h | 11 | ||||
| -rw-r--r-- | kernel/rcuclassic.c | 337 | ||||
| -rw-r--r-- | kernel/rcupreempt.c | 8 | ||||
| -rw-r--r-- | kernel/rcupreempt_trace.c | 7 | ||||
| -rw-r--r-- | lib/Kconfig.debug | 13 |
12 files changed, 337 insertions, 134 deletions
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt index cf5562cbe35..6e253407b3d 100644 --- a/Documentation/RCU/checklist.txt +++ b/Documentation/RCU/checklist.txt @@ -210,7 +210,7 @@ over a rather long period of time, but improvements are always welcome! number of updates per grace period. 9. All RCU list-traversal primitives, which include - rcu_dereference(), list_for_each_rcu(), list_for_each_entry_rcu(), + rcu_dereference(), list_for_each_entry_rcu(), list_for_each_continue_rcu(), and list_for_each_safe_rcu(), must be either within an RCU read-side critical section or must be protected by appropriate update-side locks. RCU diff --git a/Documentation/RCU/rcuref.txt b/Documentation/RCU/rcuref.txt index 451de2ad832..4202ad09313 100644 --- a/Documentation/RCU/rcuref.txt +++ b/Documentation/RCU/rcuref.txt @@ -29,9 +29,9 @@ release_referenced() delete() } If this list/array is made lock free using RCU as in changing the -write_lock() in add() and delete() to spin_lock and changing read_lock -in search_and_reference to rcu_read_lock(), the atomic_get in -search_and_reference could potentially hold reference to an element which +write_lock() in add() and delete() to spin_lock() and changing read_lock() +in search_and_reference() to rcu_read_lock(), the atomic_inc() in +search_and_reference() could potentially hold reference to an element which has already been deleted from the list/array. Use atomic_inc_not_zero() in this scenario as follows: @@ -40,20 +40,20 @@ add() search_and_reference() { { alloc_object rcu_read_lock(); ... search_for_element - atomic_set(&el->rc, 1); if (atomic_inc_not_zero(&el->rc)) { - write_lock(&list_lock); rcu_read_unlock(); + atomic_set(&el->rc, 1); if (!atomic_inc_not_zero(&el->rc)) { + spin_lock(&list_lock); rcu_read_unlock(); return FAIL; add_element } ... ... - write_unlock(&list_lock); rcu_read_unlock(); + spin_unlock(&list_lock); rcu_read_unlock(); } } 3. 4. release_referenced() delete() { { - ... write_lock(&list_lock); + ... spin_lock(&list_lock); if (atomic_dec_and_test(&el->rc)) ... call_rcu(&el->head, el_free); delete_element - ... write_unlock(&list_lock); + ... spin_unlock(&list_lock); } ... if (atomic_dec_and_test(&el->rc)) call_rcu(&el->head, el_free); diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt index e04d643a9f5..96170824a71 100644 --- a/Documentation/RCU/whatisRCU.txt +++ b/Documentation/RCU/whatisRCU.txt @@ -786,8 +786,6 @@ RCU pointer/list traversal: list_for_each_entry_rcu hlist_for_each_entry_rcu - list_for_each_rcu (to be deprecated in favor of - list_for_each_entry_rcu) list_for_each_continue_rcu (to be deprecated in favor of new list_for_each_entry_continue_rcu) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index c8bd2daf95e..8322141ee48 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -190,7 +190,9 @@ extern void __chk_io_ptr(const volatile void __iomem *); * ACCESS_ONCE() in different C statements. * * This macro does absolutely -nothing- to prevent the CPU from reordering, - * merging, or refetching absolutely anything at any time. + * merging, or refetching absolutely anything at any time. Its main intended + * use is to mediate communication between process-level code and irq/NMI + * handlers, all running on the same CPU. */ #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) diff --git a/include/linux/rcuclassic.h b/include/linux/rcuclassic.h index 4ab84362272..5f89b62e698 100644 --- a/include/linux/rcuclassic.h +++ b/include/linux/rcuclassic.h @@ -40,12 +40,21 @@ #include <linux/cpumask.h> #include <linux/seqlock.h> +#ifdef CONFIG_RCU_CPU_STALL_DETECTOR +#define RCU_SECONDS_TILL_STALL_CHECK ( 3 * HZ) /* for rcp->jiffies_stall */ +#define RCU_SECONDS_TILL_STALL_RECHECK (30 * HZ) /* for rcp->jiffies_stall */ +#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ /* Global control variables for rcupdate callback mechanism. */ struct rcu_ctrlblk { long cur; /* Current batch number. */ long completed; /* Number of the last completed batch */ - int next_pending; /* Is the next batch already waiting? */ + long pending; /* Number of the last pending batch */ +#ifdef CONFIG_RCU_CPU_STALL_DETECTOR + unsigned long gp_start; /* Time at which GP started in jiffies. */ + unsigned long jiffies_stall; + /* Time at which to check for CPU stalls. */ +#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ int signaled; @@ -66,11 +75,7 @@ static inline int rcu_batch_after(long a, long b) return (a - b) > 0; } -/* - * Per-CPU data for Read-Copy UPdate. - * nxtlist - new callbacks are added here - * curlist - current batch for which quiescent cycle started if any - */ +/* Per-CPU data for Read-Copy UPdate. */ struct rcu_data { /* 1) quiescent state handling : */ long quiescbatch; /* Batch # for grace period */ @@ -78,12 +83,24 @@ struct rcu_data { int qs_pending; /* core waits for quiesc state */ /* 2) batch handling */ - long batch; /* Batch # for current RCU batch */ + /* + * if nxtlist is not NULL, then: + * batch: + * The batch # for the last entry of nxtlist + * [*nxttail[1], NULL = *nxttail[2]): + * Entries that batch # <= batch + * [*nxttail[0], *nxttail[1]): + * Entries that batch # <= batch - 1 + * [nxtlist, *nxttail[0]): + * Entries that batch # <= batch - 2 + * The grace period for these entries has completed, and + * the other grace-period-completed entries may be moved + * here temporarily in rcu_process_callbacks(). + */ + long batch; struct rcu_head *nxtlist; - struct rcu_head **nxttail; + struct rcu_head **nxttail[3]; long qlen; /* # of queued callbacks */ - struct rcu_head *curlist; - struct rcu_head **curtail; struct rcu_head *donelist; struct rcu_head **donetail; long blimit; /* Upper limit on a processed batch */ diff --git a/include/linux/rculist.h b/include/linux/rculist.h index eb4443c7e05..e649bd3f2c9 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -198,20 +198,6 @@ static inline void list_splice_init_rcu(struct list_head *list, at->prev = last; } -/** - * list_for_each_rcu - iterate over an rcu-protected list - * @pos: the &struct list_head to use as a loop cursor. - * @head: the head for your list. - * - * This list-traversal primitive may safely run concurrently with - * the _rcu list-mutation primitives such as list_add_rcu() - * as long as the traversal is guarded by rcu_read_lock(). - */ -#define list_for_each_rcu(pos, head) \ - for (pos = rcu_dereference((head)->next); \ - prefetch(pos->next), pos != (head); \ - pos = rcu_dereference(pos->next)) - #define __list_for_each_rcu(pos, head) \ for (pos = rcu_dereference((head)->next); \ pos != (head); \ diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index e8b4039cfb2..86f1f5e43e3 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -133,6 +133,26 @@ struct rcu_head { #define rcu_read_unlock_bh() __rcu_read_unlock_bh() /** + * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section + * + * Should be used with either + * - synchronize_sched() + * or + * - call_rcu_sched() and rcu_barrier_sched() + * on the write-side to insure proper synchronization. + */ +#define rcu_read_lock_sched() preempt_disable() + +/* + * rcu_read_unlock_sched - marks the end of a RCU-classic critical section + * + * See rcu_read_lock_sched for more information. + */ +#define rcu_read_unlock_sched() preempt_enable() + + + +/** * rcu_dereference - fetch an RCU-protected pointer in an * RCU read-side critical section. This pointer may later * be safely dereferenced. diff --git a/include/linux/rcupreempt.h b/include/linux/rcupreempt.h index 0967f03b070..3e05c09b54a 100644 --- a/include/linux/rcupreempt.h +++ b/include/linux/rcupreempt.h @@ -57,7 +57,13 @@ static inline void rcu_qsctr_inc(int cpu) rdssp->sched_qs++; } #define rcu_bh_qsctr_inc(cpu) -#define call_rcu_bh(head, rcu) call_rcu(head, rcu) + +/* + * Someone might want to pass call_rcu_bh as a function pointer. + * So this needs to just be a rename and not a macro function. + * (no parentheses) + */ +#define call_rcu_bh call_rcu /** * call_rcu_sched - Queue RCU callback for invocation after sched grace period. @@ -111,7 +117,6 @@ extern struct rcupreempt_trace *rcupreempt_trace_cpu(int cpu); struct softirq_action; #ifdef CONFIG_NO_HZ -DECLARE_PER_CPU(struct rcu_dyntick_sched, rcu_dyntick_sched); static inline void rcu_enter_nohz(void) { @@ -126,8 +131,8 @@ static inline void rcu_exit_nohz(void) { static DEFINE_RATELIMIT_STATE(rs, 10 * HZ, 1); - smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */ __get_cpu_var(rcu_dyntick_sched).dynticks++; + smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */ WARN_ON_RATELIMIT(!(__get_cpu_var(rcu_dyntick_sched).dynticks & 0x1), &rs); } diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c index aad93cdc9f6..37f72e55154 100644 --- a/kernel/rcuclassic.c +++ b/kernel/rcuclassic.c @@ -47,6 +47,7 @@ #include <linux/notifier.h> #include <linux/cpu.h> #include <linux/mutex.h> +#include <linux/time.h> #ifdef CONFIG_DEBUG_LOCK_ALLOC static struct lock_class_key rcu_lock_key; @@ -60,12 +61,14 @@ EXPORT_SYMBOL_GPL(rcu_lock_map); static struct rcu_ctrlblk rcu_ctrlblk = { .cur = -300, .completed = -300, + .pending = -300, .lock = __SPIN_LOCK_UNLOCKED(&rcu_ctrlblk.lock), .cpumask = CPU_MASK_NONE, }; static struct rcu_ctrlblk rcu_bh_ctrlblk = { .cur = -300, .completed = -300, + .pending = -300, .lock = __SPIN_LOCK_UNLOCKED(&rcu_bh_ctrlblk.lock), .cpumask = CPU_MASK_NONE, }; @@ -83,7 +86,10 @@ static void force_quiescent_state(struct rcu_data *rdp, { int cpu; cpumask_t cpumask; + unsigned long flags; + set_need_resched(); + spin_lock_irqsave(&rcp->lock, flags); if (unlikely(!rcp->signaled)) { rcp->signaled = 1; /* @@ -109,6 +115,7 @@ static void force_quiescent_state(struct rcu_data *rdp, for_each_cpu_mask_nr(cpu, cpumask) smp_send_reschedule(cpu); } + spin_unlock_irqrestore(&rcp->lock, flags); } #else static inline void force_quiescent_state(struct rcu_data *rdp, @@ -118,6 +125,126 @@ static inline void force_quiescent_state(struct rcu_data *rdp, } #endif +static void __call_rcu(struct rcu_head *head, struct rcu_ctrlblk *rcp, + struct rcu_data *rdp) +{ + long batch; + + head->next = NULL; + smp_mb(); /* Read of rcu->cur must happen after any change by caller. */ + + /* + * Determine the batch number of this callback. + * + * Using ACCESS_ONCE to avoid the following error when gcc eliminates + * local variable "batch" and emits codes like this: + * 1) rdp->batch = rcp->cur + 1 # gets old value + * ...... + * 2)rcu_batch_after(rcp->cur + 1, rdp->batch) # gets new value + * then [*nxttail[0], *nxttail[1]) may contain callbacks + * that batch# = rdp->batch, see the comment of struct rcu_data. + */ + batch = ACCESS_ONCE(rcp->cur) + 1; + + if (rdp->nxtlist && rcu_batch_after(batch, rdp->batch)) { + /* process callbacks */ + rdp->nxttail[0] = rdp->nxttail[1]; + rdp->nxttail[1] = rdp->nxttail[2]; + if (rcu_batch_after(batch - 1, rdp->batch)) + rdp->nxttail[0] = rdp->nxttail[2]; + } + + rdp->batch = batch; + *rdp->nxttail[2] = head; + rdp->nxttail[2] = &head->next; + + if (unlikely(++rdp->qlen > qhimark)) { + rdp->blimit = INT_MAX; + force_quiescent_state(rdp, &rcu_ctrlblk); + } +} + +#ifdef CONFIG_RCU_CPU_STALL_DETECTOR + +static void record_gp_stall_check_time(struct rcu_ctrlblk *rcp) +{ + rcp->gp_start = jiffies; + rcp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK; +} + +static void print_other_cpu_stall(struct rcu_ctrlblk *rcp) +{ + int cpu; + long delta; + unsigned long flags; + + /* Only let one CPU complain about others per time interval. */ + + spin_lock_irqsave(&rcp->lock, flags); + delta = jiffies - rcp->jiffies_stall; + if (delta < 2 || rcp->cur != rcp->completed) { + spin_unlock_irqrestore(&rcp->lock, flags); + return; + } + rcp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK; + spin_unlock_irqrestore(&rcp->lock, flags); + + /* OK, time to rat on our buddy... */ + + printk(KERN_ERR "RCU detected CPU stalls:"); + for_each_possible_cpu(cpu) { + if (cpu_isset(cpu, rcp->cpumask)) + printk(" %d", cpu); + } + printk(" (detected by %d, t=%ld jiffies)\n", + smp_processor_id(), (long)(jiffies - rcp->gp_start)); +} + +static void print_cpu_stall(struct rcu_ctrlblk *rcp) +{ + unsigned long flags; + + printk(KERN_ERR "RCU detected CPU %d stall (t=%lu/%lu jiffies)\n", + smp_processor_id(), jiffies, + jiffies - rcp->gp_start); + dump_stack(); + spin_lock_irqsave(&rcp->lock, flags); + if ((long)(jiffies - rcp->jiffies_stall) >= 0) + rcp->jiffies_stall = + jiffies + RCU_SECONDS_TILL_STALL_RECHECK; + spin_unlock_irqrestore(&rcp->lock, flags); + set_need_resched(); /* kick ourselves to get things going. */ +} + +static void check_cpu_stall(struct rcu_ctrlblk *rcp) +{ + long delta; + + delta = jiffies - rcp->jiffies_stall; + if (cpu_isset(smp_processor_id(), rcp->cpumask) && delta >= 0) { + + /* We haven't checked in, so go dump stack. */ + print_cpu_stall(rcp); + + } else if (rcp->cur != rcp->completed && delta >= 2) { + + /* They had two seconds to dump stack, so complain. */ + print_other_cpu_stall(rcp); + } +} + +#else /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ + +static void record_gp_stall_check_time(struct rcu_ctrlblk *rcp) +{ +} + +static inline void check_cpu_stall(struct rcu_ctrlblk *rcp) +{ +} + +#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ + /** * call_rcu - Queue an RCU callback for invocation after a grace period. * @head: structure to be used for queueing the RCU updates. @@ -133,18 +260,10 @@ 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 = &__get_cpu_var(rcu_data); - *rdp->nxttail = head; - rdp->nxttail = &head->next; - if (unlikely(++rdp->qlen > qhimark)) { - rdp->blimit = INT_MAX; - force_quiescent_state(rdp, &rcu_ctrlblk); - } + __call_rcu(head, &rcu_ctrlblk, &__get_cpu_var(rcu_data)); local_irq_restore(flags); } EXPORT_SYMBOL_GPL(call_rcu); @@ -169,20 +288,10 @@ void 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; - - if (unlikely(++rdp->qlen > qhimark)) { - rdp->blimit = INT_MAX; - force_quiescent_state(rdp, &rcu_bh_ctrlblk); - } - + __call_rcu(head, &rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data)); local_irq_restore(flags); } EXPORT_SYMBOL_GPL(call_rcu_bh); @@ -211,12 +320,6 @@ EXPORT_SYMBOL_GPL(rcu_batches_completed_bh); static inline void raise_rcu_softirq(void) { raise_softirq(RCU_SOFTIRQ); - /* - * The smp_mb() here is required to ensure that this cpu's - * __rcu_process_callbacks() reads the most recently updated - * value of rcu->cur. - */ - smp_mb(); } /* @@ -225,6 +328,7 @@ static inline void raise_rcu_softirq(void) */ static void rcu_do_batch(struct rcu_data *rdp) { + unsigned long flags; struct rcu_head *next, *list; int count = 0; @@ -239,9 +343,9 @@ static void rcu_do_batch(struct rcu_data *rdp) } rdp->donelist = list; - local_irq_disable(); + local_irq_save(flags); rdp->qlen -= count; - local_irq_enable(); + local_irq_restore(flags); if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark) rdp->blimit = blimit; @@ -269,6 +373,7 @@ static void rcu_do_batch(struct rcu_data *rdp) * 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. @@ -276,15 +381,10 @@ static void rcu_do_batch(struct rcu_data *rdp) */ static void rcu_start_batch(struct rcu_ctrlblk *rcp) { - if (rcp->next_pending && + if (rcp->cur != rcp->pending && rcp->completed == rcp->cur) { - 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++; + record_gp_stall_check_time(rcp); /* * Accessing nohz_cpu_mask before incrementing rcp->cur needs a @@ -322,6 +422,8 @@ static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp) static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp, struct rcu_data *rdp) { + unsigned long flags; + if (rdp->quiescbatch != rcp->cur) { /* start new grace period: */ rdp->qs_pending = 1; @@ -345,7 +447,7 @@ static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp, return; rdp->qs_pending = 0; - spin_lock(&rcp->lock); + spin_lock_irqsave(&rcp->lock, flags); /* * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync * during cpu startup. Ignore the quiescent state. @@ -353,7 +455,7 @@ static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp, if (likely(rdp->quiescbatch == rcp->cur)) cpu_quiet(rdp->cpu, rcp); - spin_unlock(&rcp->lock); + spin_unlock_irqrestore(&rcp->lock, flags); } @@ -364,33 +466,38 @@ static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp, * 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) + struct rcu_head **tail, long batch) { - local_irq_disable(); - *this_rdp->nxttail = list; - if (list) - this_rdp->nxttail = tail; - local_irq_enable(); + unsigned long flags; + + if (list) { + local_irq_save(flags); + this_rdp->batch = batch; + *this_rdp->nxttail[2] = list; + this_rdp->nxttail[2] = tail; + local_irq_restore(flags); + } } static void __rcu_offline_cpu(struct rcu_data *this_rdp, struct rcu_ctrlblk *rcp, struct rcu_data *rdp) { - /* if the cpu going offline owns the grace period + unsigned long flags; + + /* + * if the cpu going offline owns the grace period * we can block indefinitely waiting for it, so flush * it here */ - spin_lock_bh(&rcp->lock); + spin_lock_irqsave(&rcp->lock, flags); if (rcp->cur != rcp->completed) cpu_quiet(rdp->cpu, rcp); - spin_unlock_bh(&rcp->lock); - rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail); - rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail); - rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail); + rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail, rcp->cur + 1); + rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail[2], rcp->cur + 1); + spin_unlock(&rcp->lock); - local_irq_disable(); this_rdp->qlen += rdp->qlen; - local_irq_enable(); + local_irq_restore(flags); } static void rcu_offline_cpu(int cpu) @@ -420,38 +527,52 @@ static void rcu_offline_cpu(int cpu) static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp, 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; - } + unsigned long flags; + long completed_snap; - if (rdp->nxtlist && !rdp->curlist) { - local_irq_disable(); - rdp->curlist = rdp->nxtlist; - rdp->curtail = rdp->nxttail; - rdp->nxtlist = NULL; - rdp->nxttail = &rdp->nxtlist; - local_irq_enable(); + if (rdp->nxtlist) { + local_irq_save(flags); + completed_snap = ACCESS_ONCE(rcp->completed); /* - * start the next batch of callbacks + * move the other grace-period-completed entries to + * [rdp->nxtlist, *rdp->nxttail[0]) temporarily */ + if (!rcu_batch_before(completed_snap, rdp->batch)) + rdp->nxttail[0] = rdp->nxttail[1] = rdp->nxttail[2]; + else if (!rcu_batch_before(completed_snap, rdp->batch - 1)) + rdp->nxttail[0] = rdp->nxttail[1]; - /* determine batch number */ - rdp->batch = rcp->cur + 1; - /* see the comment and corresponding wmb() in - * the rcu_start_batch() + /* + * the grace period for entries in + * [rdp->nxtlist, *rdp->nxttail[0]) has completed and + * move these entries to donelist */ - smp_rmb(); + if (rdp->nxttail[0] != &rdp->nxtlist) { + *rdp->donetail = rdp->nxtlist; + rdp->donetail = rdp->nxttail[0]; + rdp->nxtlist = *rdp->nxttail[0]; + *rdp->donetail = NULL; + + if (rdp->nxttail[1] == rdp->nxttail[0]) + rdp->nxttail[1] = &rdp->nxtlist; + if (rdp->nxttail[2] == rdp->nxttail[0]) + rdp->nxttail[2] = &rdp->nxtlist; + rdp->nxttail[0] = &rdp->nxtlist; + } + + local_irq_restore(flags); + + if (rcu_batch_after(rdp->batch, rcp->pending)) { + unsigned long flags2; - if (!rcp->next_pending) { /* and start it/schedule start if it's a new batch */ - spin_lock(&rcp->lock); - rcp->next_pending = 1; - rcu_start_batch(rcp); - spin_unlock(&rcp->lock); + spin_lock_irqsave(&rcp->lock, flags2); + if (rcu_batch_after(rdp->batch, rcp->pending)) { + rcp->pending = rdp->batch; + rcu_start_batch(rcp); + } + spin_unlock_irqrestore(&rcp->lock, flags2); } } @@ -462,21 +583,53 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp, static void rcu_process_callbacks(struct softirq_action *unused) { + /* + * Memory references from any prior RCU read-side critical sections + * executed by the interrupted code must be see before any RCU + * grace-period manupulations below. + */ + + smp_mb(); /* See above block comment. */ + __rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data)); __rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data)); + + /* + * Memory references from any later RCU read-side critical sections + * executed by the interrupted code must be see after any RCU + * grace-period manupulations above. + */ + + smp_mb(); /* See above block comment. */ } static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp) { - /* This cpu has pending rcu entries and the grace period - * for them has completed. - */ - if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) - return 1; + /* Check for CPU stalls, if enabled. */ + check_cpu_stall(rcp); - /* This cpu has no pending entries, but there are new entries */ - if (!rdp->curlist && rdp->nxtlist) - return 1; + if (rdp->nxtlist) { + long completed_snap = ACCESS_ONCE(rcp->completed); + + /* + * This cpu has pending rcu entries and the grace period + * for them has completed. + */ + if (!rcu_batch_before(completed_snap, rdp->batch)) + return 1; + if (!rcu_batch_before(completed_snap, rdp->batch - 1) && + rdp->nxttail[0] != rdp->nxttail[1]) + return 1; + if (rdp->nxttail[0] != &rdp->nxtlist) + return 1; + + /* + * This cpu has pending rcu entries and the new batch + * for then hasn't been started nor scheduled start + */ + if (rcu_batch_after(rdp->batch, rcp->pending)) + return 1; + } /* This cpu has finished callbacks to invoke */ if (rdp->donelist) @@ -512,9 +665,15 @@ int rcu_needs_cpu(int cpu) struct rcu_data *rdp = &per_cpu(rcu_data, cpu); struct rcu_data *rdp_bh = &per_cpu(rcu_bh_data, cpu); - return (!!rdp->curlist || !!rdp_bh->curlist || rcu_pending(cpu)); + return !!rdp->nxtlist || !!rdp_bh->nxtlist || rcu_pending(cpu); } +/* + * Top-level function driving RCU grace-period detection, normally + * invoked from the scheduler-clock interrupt. This function simply + * increments counters that are read only from softirq by this same + * CPU, so there are no memory barriers required. + */ void rcu_check_callbacks(int cpu, int user) { if (user || @@ -558,14 +717,17 @@ void rcu_check_callbacks(int cpu, int user) static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp, struct rcu_data *rdp) { + unsigned long flags; + + spin_lock_irqsave(&rcp->lock, flags); memset(rdp, 0, sizeof(*rdp)); - rdp->curtail = &rdp->curlist; - rdp->nxttail = &rdp->nxtlist; + rdp->nxttail[0] = rdp->nxttail[1] = rdp->nxttail[2] = &rdp->nxtlist; rdp->donetail = &rdp->donelist; rdp->quiescbatch = rcp->completed; rdp->qs_pending = 0; rdp->cpu = cpu; rdp->blimit = blimit; + spin_unlock_irqrestore(&rcp->lock, flags); } static void __cpuinit rcu_online_cpu(int cpu) @@ -610,6 +772,9 @@ static struct notifier_block __cpuinitdata rcu_nb = { */ void __init __rcu_init(void) { +#ifdef CONFIG_RCU_CPU_STALL_DETECTOR + printk(KERN_INFO "RCU-based detection of stalled CPUs is enabled.\n"); +#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long)smp_processor_id()); /* Register notifier for non-boot CPUs */ diff --git a/kernel/rcupreempt.c b/kernel/rcupreempt.c index 27827931ca0..ca4bbbe04aa 100644 --- a/kernel/rcupreempt.c +++ b/kernel/rcupreempt.c @@ -59,14 +59,6 @@ #include <linux/rcupreempt_trace.h> /* - * Macro that prevents the compiler from reordering accesses, but does - * absolutely -nothing- to prevent CPUs from reordering. This is used - * only to mediate communication between mainline code and hardware - * interrupt and NMI handlers. - */ -#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) - -/* * PREEMPT_RCU data structures. */ diff --git a/kernel/rcupreempt_trace.c b/kernel/rcupreempt_trace.c index 5edf82c34bb..35c2d3360ec 100644 --- a/kernel/rcupreempt_trace.c +++ b/kernel/rcupreempt_trace.c @@ -308,11 +308,16 @@ out: static int __init rcupreempt_trace_init(void) { + int ret; + mutex_init(&rcupreempt_trace_mutex); rcupreempt_trace_buf = kmalloc(RCUPREEMPT_TRACE_BUF_SIZE, GFP_KERNEL); if (!rcupreempt_trace_buf) return 1; - return rcupreempt_debugfs_init(); + ret = rcupreempt_debugfs_init(); + if (ret) + kfree(rcupreempt_trace_buf); + return ret; } static void __exit rcupreempt_trace_cleanup(void) diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 7d7a31d0dde..ce697e0b319 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -597,6 +597,19 @@ config RCU_TORTURE_TEST_RUNNABLE Say N here if you want the RCU torture tests to start only after being manually enabled via /proc. +config RCU_CPU_STALL_DETECTOR + bool "Check for stalled CPUs delaying RCU grace periods" + depends on CLASSIC_RCU + default n + help + This option causes RCU to printk information on which + CPUs are delaying the current grace period, but only when + the grace period extends for excessive time periods. + + Say Y if you want RCU to perform such checks. + + Say N if you are unsure. + config KPROBES_SANITY_TEST bool "Kprobes sanity tests" depends on DEBUG_KERNEL |