diff options
Diffstat (limited to 'kernel/rcu/tree.c')
| -rw-r--r-- | kernel/rcu/tree.c | 330 |
1 files changed, 252 insertions, 78 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 79aea7df4345..6bb8e72bc815 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -76,6 +76,7 @@ /* Data structures. */ static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = { + .gpwrap = true, #ifdef CONFIG_RCU_NOCB_CPU .cblist.flags = SEGCBLIST_RCU_CORE, #endif @@ -1755,6 +1756,8 @@ static noinline void rcu_gp_cleanup(void) dump_blkd_tasks(rnp, 10); WARN_ON_ONCE(rnp->qsmask); WRITE_ONCE(rnp->gp_seq, new_gp_seq); + if (!rnp->parent) + smp_mb(); // Order against failing poll_state_synchronize_rcu_full(). rdp = this_cpu_ptr(&rcu_data); if (rnp == rdp->mynode) needgp = __note_gp_changes(rnp, rdp) || needgp; @@ -2341,8 +2344,8 @@ void rcu_sched_clock_irq(int user) rcu_flavor_sched_clock_irq(user); if (rcu_pending(user)) invoke_rcu_core(); - if (user) - rcu_tasks_classic_qs(current, false); + if (user || rcu_is_cpu_rrupt_from_idle()) + rcu_note_voluntary_context_switch(current); lockdep_assert_irqs_disabled(); trace_rcu_utilization(TPS("End scheduler-tick")); @@ -2832,7 +2835,7 @@ EXPORT_SYMBOL_GPL(call_rcu); /* Maximum number of jiffies to wait before draining a batch. */ -#define KFREE_DRAIN_JIFFIES (HZ / 50) +#define KFREE_DRAIN_JIFFIES (5 * HZ) #define KFREE_N_BATCHES 2 #define FREE_N_CHANNELS 2 @@ -3093,6 +3096,21 @@ need_offload_krc(struct kfree_rcu_cpu *krcp) return !!krcp->head; } +static void +schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp) +{ + long delay, delay_left; + + delay = READ_ONCE(krcp->count) >= KVFREE_BULK_MAX_ENTR ? 1:KFREE_DRAIN_JIFFIES; + if (delayed_work_pending(&krcp->monitor_work)) { + delay_left = krcp->monitor_work.timer.expires - jiffies; + if (delay < delay_left) + mod_delayed_work(system_wq, &krcp->monitor_work, delay); + return; + } + queue_delayed_work(system_wq, &krcp->monitor_work, delay); +} + /* * This function is invoked after the KFREE_DRAIN_JIFFIES timeout. */ @@ -3150,7 +3168,7 @@ static void kfree_rcu_monitor(struct work_struct *work) // work to repeat an attempt. Because previous batches are // still in progress. if (need_offload_krc(krcp)) - schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES); + schedule_delayed_monitor_work(krcp); raw_spin_unlock_irqrestore(&krcp->lock, flags); } @@ -3183,15 +3201,16 @@ static void fill_page_cache_func(struct work_struct *work) bnode = (struct kvfree_rcu_bulk_data *) __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN); - if (bnode) { - raw_spin_lock_irqsave(&krcp->lock, flags); - pushed = put_cached_bnode(krcp, bnode); - raw_spin_unlock_irqrestore(&krcp->lock, flags); + if (!bnode) + break; - if (!pushed) { - free_page((unsigned long) bnode); - break; - } + raw_spin_lock_irqsave(&krcp->lock, flags); + pushed = put_cached_bnode(krcp, bnode); + raw_spin_unlock_irqrestore(&krcp->lock, flags); + + if (!pushed) { + free_page((unsigned long) bnode); + break; } } @@ -3338,7 +3357,7 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) // Set timer to drain after KFREE_DRAIN_JIFFIES. if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING) - schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES); + schedule_delayed_monitor_work(krcp); unlock_return: krc_this_cpu_unlock(krcp, flags); @@ -3371,7 +3390,7 @@ kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc) atomic_set(&krcp->backoff_page_cache_fill, 1); } - return count; + return count == 0 ? SHRINK_EMPTY : count; } static unsigned long @@ -3414,49 +3433,27 @@ void __init kfree_rcu_scheduler_running(void) raw_spin_lock_irqsave(&krcp->lock, flags); if (need_offload_krc(krcp)) - schedule_delayed_work_on(cpu, &krcp->monitor_work, KFREE_DRAIN_JIFFIES); + schedule_delayed_monitor_work(krcp); raw_spin_unlock_irqrestore(&krcp->lock, flags); } } /* * During early boot, any blocking grace-period wait automatically - * implies a grace period. Later on, this is never the case for PREEMPTION. + * implies a grace period. * - * However, because a context switch is a grace period for !PREEMPTION, 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_rcu() or synchronize_rcu_expedited(). 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. + * Later on, this could in theory be the case for kernels built with + * CONFIG_SMP=y && CONFIG_PREEMPTION=y running on a single CPU, but this + * is not a common case. Furthermore, this optimization would cause + * the rcu_gp_oldstate structure to expand by 50%, so this potential + * grace-period optimization is ignored once the scheduler is running. */ static int rcu_blocking_is_gp(void) { - int ret; - - // Invoking preempt_model_*() too early gets a splat. - if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE || - preempt_model_full() || preempt_model_rt()) - return rcu_scheduler_active == RCU_SCHEDULER_INACTIVE; + if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) + return false; might_sleep(); /* Check for RCU read-side critical section. */ - preempt_disable(); - /* - * If the rcu_state.n_online_cpus counter is equal to one, - * there is only one CPU, and that CPU sees all prior accesses - * made by any CPU that was online at the time of its access. - * Furthermore, if this counter is equal to one, its value cannot - * change until after the preempt_enable() below. - * - * Furthermore, if rcu_state.n_online_cpus is equal to one here, - * all later CPUs (both this one and any that come online later - * on) are guaranteed to see all accesses prior to this point - * in the code, without the need for additional memory barriers. - * Those memory barriers are provided by CPU-hotplug code. - */ - ret = READ_ONCE(rcu_state.n_online_cpus) <= 1; - preempt_enable(); - return ret; + return true; } /** @@ -3499,30 +3496,59 @@ static int rcu_blocking_is_gp(void) */ void synchronize_rcu(void) { + unsigned long flags; + struct rcu_node *rnp; + 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() in RCU read-side critical section"); - if (rcu_blocking_is_gp()) { - // Note well that this code runs with !PREEMPT && !SMP. - // In addition, all code that advances grace periods runs at - // process level. Therefore, this normal GP overlaps with - // other normal GPs only by being fully nested within them, - // which allows reuse of ->gp_seq_polled_snap. - rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_snap); - rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_snap); - if (rcu_init_invoked()) - cond_resched_tasks_rcu_qs(); - return; // Context allows vacuous grace periods. + if (!rcu_blocking_is_gp()) { + if (rcu_gp_is_expedited()) + synchronize_rcu_expedited(); + else + wait_rcu_gp(call_rcu); + return; } - if (rcu_gp_is_expedited()) - synchronize_rcu_expedited(); - else - wait_rcu_gp(call_rcu); + + // Context allows vacuous grace periods. + // Note well that this code runs with !PREEMPT && !SMP. + // In addition, all code that advances grace periods runs at + // process level. Therefore, this normal GP overlaps with other + // normal GPs only by being fully nested within them, which allows + // reuse of ->gp_seq_polled_snap. + rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_snap); + rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_snap); + + // Update the normal grace-period counters to record + // this grace period, but only those used by the boot CPU. + // The rcu_scheduler_starting() will take care of the rest of + // these counters. + local_irq_save(flags); + WARN_ON_ONCE(num_online_cpus() > 1); + rcu_state.gp_seq += (1 << RCU_SEQ_CTR_SHIFT); + for (rnp = this_cpu_ptr(&rcu_data)->mynode; rnp; rnp = rnp->parent) + rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq; + local_irq_restore(flags); } EXPORT_SYMBOL_GPL(synchronize_rcu); /** + * get_completed_synchronize_rcu_full - Return a full pre-completed polled state cookie + * @rgosp: Place to put state cookie + * + * Stores into @rgosp a value that will always be treated by functions + * like poll_state_synchronize_rcu_full() as a cookie whose grace period + * has already completed. + */ +void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp) +{ + rgosp->rgos_norm = RCU_GET_STATE_COMPLETED; + rgosp->rgos_exp = RCU_GET_STATE_COMPLETED; +} +EXPORT_SYMBOL_GPL(get_completed_synchronize_rcu_full); + +/** * get_state_synchronize_rcu - Snapshot current RCU state * * Returns a cookie that is used by a later call to cond_synchronize_rcu() @@ -3541,21 +3567,42 @@ unsigned long get_state_synchronize_rcu(void) EXPORT_SYMBOL_GPL(get_state_synchronize_rcu); /** - * start_poll_synchronize_rcu - Snapshot and start RCU grace period + * get_state_synchronize_rcu_full - Snapshot RCU state, both normal and expedited + * @rgosp: location to place combined normal/expedited grace-period state * - * Returns a cookie that is used by a later call to cond_synchronize_rcu() - * or poll_state_synchronize_rcu() to determine whether or not a full - * grace period has elapsed in the meantime. If the needed grace period - * is not already slated to start, notifies RCU core of the need for that - * grace period. + * Places the normal and expedited grace-period states in @rgosp. This + * state value can be passed to a later call to cond_synchronize_rcu_full() + * or poll_state_synchronize_rcu_full() to determine whether or not a + * grace period (whether normal or expedited) has elapsed in the meantime. + * The rcu_gp_oldstate structure takes up twice the memory of an unsigned + * long, but is guaranteed to see all grace periods. In contrast, the + * combined state occupies less memory, but can sometimes fail to take + * grace periods into account. * - * Interrupts must be enabled for the case where it is necessary to awaken - * the grace-period kthread. + * This does not guarantee that the needed grace period will actually + * start. */ -unsigned long start_poll_synchronize_rcu(void) +void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp) +{ + struct rcu_node *rnp = rcu_get_root(); + + /* + * Any prior manipulation of RCU-protected data must happen + * before the loads from ->gp_seq and ->expedited_sequence. + */ + smp_mb(); /* ^^^ */ + rgosp->rgos_norm = rcu_seq_snap(&rnp->gp_seq); + rgosp->rgos_exp = rcu_seq_snap(&rcu_state.expedited_sequence); +} +EXPORT_SYMBOL_GPL(get_state_synchronize_rcu_full); + +/* + * Helper function for start_poll_synchronize_rcu() and + * start_poll_synchronize_rcu_full(). + */ +static void start_poll_synchronize_rcu_common(void) { unsigned long flags; - unsigned long gp_seq = get_state_synchronize_rcu(); bool needwake; struct rcu_data *rdp; struct rcu_node *rnp; @@ -3575,17 +3622,57 @@ unsigned long start_poll_synchronize_rcu(void) raw_spin_unlock_irqrestore_rcu_node(rnp, flags); if (needwake) rcu_gp_kthread_wake(); +} + +/** + * start_poll_synchronize_rcu - Snapshot and start RCU grace period + * + * Returns a cookie that is used by a later call to cond_synchronize_rcu() + * or poll_state_synchronize_rcu() to determine whether or not a full + * grace period has elapsed in the meantime. If the needed grace period + * is not already slated to start, notifies RCU core of the need for that + * grace period. + * + * Interrupts must be enabled for the case where it is necessary to awaken + * the grace-period kthread. + */ +unsigned long start_poll_synchronize_rcu(void) +{ + unsigned long gp_seq = get_state_synchronize_rcu(); + + start_poll_synchronize_rcu_common(); return gp_seq; } EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu); /** - * poll_state_synchronize_rcu - Conditionally wait for an RCU grace period + * start_poll_synchronize_rcu_full - Take a full snapshot and start RCU grace period + * @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full() * + * Places the normal and expedited grace-period states in *@rgos. This + * state value can be passed to a later call to cond_synchronize_rcu_full() + * or poll_state_synchronize_rcu_full() to determine whether or not a + * grace period (whether normal or expedited) has elapsed in the meantime. + * If the needed grace period is not already slated to start, notifies + * RCU core of the need for that grace period. + * + * Interrupts must be enabled for the case where it is necessary to awaken + * the grace-period kthread. + */ +void start_poll_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp) +{ + get_state_synchronize_rcu_full(rgosp); + + start_poll_synchronize_rcu_common(); +} +EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_full); + +/** + * poll_state_synchronize_rcu - Has the specified RCU grace period completed? * @oldstate: value from get_state_synchronize_rcu() or start_poll_synchronize_rcu() * * If a full RCU grace period has elapsed since the earlier call from - * which oldstate was obtained, return @true, otherwise return @false. + * which @oldstate was obtained, return @true, otherwise return @false. * If @false is returned, it is the caller's responsibility to invoke this * function later on until it does return @true. Alternatively, the caller * can explicitly wait for a grace period, for example, by passing @oldstate @@ -3594,10 +3681,11 @@ EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu); * 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 a billion grace periods (and way more on a 64-bit system!). - * Those needing to keep oldstate values for very long time periods - * (many hours even on 32-bit systems) should check them occasionally - * and either refresh them or set a flag indicating that the grace period - * has completed. + * Those needing to keep old state values for very long time periods + * (many hours even on 32-bit systems) should check them occasionally and + * either refresh them or set a flag indicating that the grace period has + * completed. Alternatively, they can use get_completed_synchronize_rcu() + * to get a guaranteed-completed grace-period state. * * This function provides the same memory-ordering guarantees that * would be provided by a synchronize_rcu() that was invoked at the call @@ -3616,8 +3704,56 @@ bool poll_state_synchronize_rcu(unsigned long oldstate) EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu); /** - * cond_synchronize_rcu - Conditionally wait for an RCU grace period + * poll_state_synchronize_rcu_full - Has the specified RCU grace period completed? + * @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full() * + * If a full RCU grace period has elapsed since the earlier call from + * which *rgosp was obtained, return @true, otherwise return @false. + * If @false is returned, it is the caller's responsibility to invoke this + * function later on until it does return @true. Alternatively, the caller + * can explicitly wait for a grace period, for example, by passing @rgosp + * to cond_synchronize_rcu() or by directly invoking synchronize_rcu(). + * + * 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 a billion grace periods (and way more on a 64-bit + * system!). Those needing to keep rcu_gp_oldstate values for very + * long time periods (many hours even on 32-bit systems) should check + * them occasionally and either refresh them or set a flag indicating + * that the grace period has completed. Alternatively, they can use + * get_completed_synchronize_rcu_full() to get a guaranteed-completed + * grace-period state. + * + * This function provides the same memory-ordering guarantees that would + * be provided by a synchronize_rcu() that was invoked at the call to + * the function that provided @rgosp, and that returned at the end of this + * function. And this guarantee requires that the root rcu_node structure's + * ->gp_seq field be checked instead of that of the rcu_state structure. + * The problem is that the just-ending grace-period's callbacks can be + * invoked between the time that the root rcu_node structure's ->gp_seq + * field is updated and the time that the rcu_state structure's ->gp_seq + * field is updated. Therefore, if a single synchronize_rcu() is to + * cause a subsequent poll_state_synchronize_rcu_full() to return @true, + * then the root rcu_node structure is the one that needs to be polled. + */ +bool poll_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp) +{ + struct rcu_node *rnp = rcu_get_root(); + + smp_mb(); // Order against root rcu_node structure grace-period cleanup. + if (rgosp->rgos_norm == RCU_GET_STATE_COMPLETED || + rcu_seq_done_exact(&rnp->gp_seq, rgosp->rgos_norm) || + rgosp->rgos_exp == RCU_GET_STATE_COMPLETED || + rcu_seq_done_exact(&rcu_state.expedited_sequence, rgosp->rgos_exp)) { + smp_mb(); /* Ensure GP ends before subsequent accesses. */ + return true; + } + return false; +} +EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu_full); + +/** + * cond_synchronize_rcu - Conditionally wait for an RCU grace period * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited() * * If a full RCU grace period has elapsed since the earlier call to @@ -3641,6 +3777,33 @@ void cond_synchronize_rcu(unsigned long oldstate) } EXPORT_SYMBOL_GPL(cond_synchronize_rcu); +/** + * cond_synchronize_rcu_full - Conditionally wait for an RCU grace period + * @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full() + * + * If a full RCU grace period has elapsed since the call to + * get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), + * or start_poll_synchronize_rcu_expedited_full() from which @rgosp was + * obtained, 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 a couple of additional grace periods should be just fine. + * + * This function provides the same memory-ordering guarantees that + * would be provided by a synchronize_rcu() that was invoked at the call + * to the function that provided @rgosp and that returned at the end of + * this function. + */ +void cond_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp) +{ + if (!poll_state_synchronize_rcu_full(rgosp)) + synchronize_rcu(); +} +EXPORT_SYMBOL_GPL(cond_synchronize_rcu_full); + /* * Check to see if there is any immediate RCU-related work to be done by * the current CPU, returning 1 if so and zero otherwise. The checks are @@ -4312,9 +4475,20 @@ early_initcall(rcu_spawn_gp_kthread); */ void rcu_scheduler_starting(void) { + unsigned long flags; + struct rcu_node *rnp; + WARN_ON(num_online_cpus() != 1); WARN_ON(nr_context_switches() > 0); rcu_test_sync_prims(); + + // Fix up the ->gp_seq counters. + local_irq_save(flags); + rcu_for_each_node_breadth_first(rnp) + rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq; + local_irq_restore(flags); + + // Switch out of early boot mode. rcu_scheduler_active = RCU_SCHEDULER_INIT; rcu_test_sync_prims(); } |