diff options
Diffstat (limited to 'kernel/rcutree.c')
| -rw-r--r-- | kernel/rcutree.c | 166 |
1 files changed, 52 insertions, 114 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index b703989..80fd02e 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -323,35 +323,6 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp) } /* - * If the specified CPU is offline, tell the caller that it is in - * a quiescent state. Otherwise, whack it with a reschedule IPI. - * Grace periods can end up waiting on an offline CPU when that - * CPU is in the process of coming online -- it will be added to the - * rcu_node bitmasks before it actually makes it online. The same thing - * can happen while a CPU is in the process of coming online. Because this - * race is quite rare, we check for it after detecting that the grace - * period has been delayed rather than checking each and every CPU - * each and every time we start a new grace period. - */ -static int rcu_implicit_offline_qs(struct rcu_data *rdp) -{ - /* - * If the CPU is offline for more than a jiffy, it is in a quiescent - * state. We can trust its state not to change because interrupts - * are disabled. The reason for the jiffy's worth of slack is to - * handle CPUs initializing on the way up and finding their way - * to the idle loop on the way down. - */ - if (cpu_is_offline(rdp->cpu) && - ULONG_CMP_LT(rdp->rsp->gp_start + 2, jiffies)) { - trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "ofl"); - rdp->offline_fqs++; - return 1; - } - return 0; -} - -/* * rcu_idle_enter_common - inform RCU that current CPU is moving towards idle * * If the new value of the ->dynticks_nesting counter now is zero, @@ -679,7 +650,7 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp) * Return true if the specified CPU has passed through a quiescent * state by virtue of being in or having passed through an dynticks * idle state since the last call to dyntick_save_progress_counter() - * for this same CPU. + * for this same CPU, or by virtue of having been offline. */ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) { @@ -703,8 +674,26 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) return 1; } - /* Go check for the CPU being offline. */ - return rcu_implicit_offline_qs(rdp); + /* + * Check for the CPU being offline, but only if the grace period + * is old enough. We don't need to worry about the CPU changing + * state: If we see it offline even once, it has been through a + * quiescent state. + * + * The reason for insisting that the grace period be at least + * one jiffy old is that CPUs that are not quite online and that + * have just gone offline can still execute RCU read-side critical + * sections. + */ + if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies)) + return 0; /* Grace period is not old enough. */ + barrier(); + if (cpu_is_offline(rdp->cpu)) { + trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "ofl"); + rdp->offline_fqs++; + return 1; + } + return 0; } static int jiffies_till_stall_check(void) @@ -761,14 +750,15 @@ static void print_other_cpu_stall(struct rcu_state *rsp) rcu_for_each_leaf_node(rsp, rnp) { raw_spin_lock_irqsave(&rnp->lock, flags); ndetected += rcu_print_task_stall(rnp); + if (rnp->qsmask != 0) { + for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++) + if (rnp->qsmask & (1UL << cpu)) { + print_cpu_stall_info(rsp, + rnp->grplo + cpu); + ndetected++; + } + } raw_spin_unlock_irqrestore(&rnp->lock, flags); - if (rnp->qsmask == 0) - continue; - for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++) - if (rnp->qsmask & (1UL << cpu)) { - print_cpu_stall_info(rsp, rnp->grplo + cpu); - ndetected++; - } } /* @@ -833,7 +823,8 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) j = ACCESS_ONCE(jiffies); js = ACCESS_ONCE(rsp->jiffies_stall); rnp = rdp->mynode; - if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) { + if (rcu_gp_in_progress(rsp) && + (ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) { /* We haven't checked in, so go dump stack. */ print_cpu_stall(rsp); @@ -1486,17 +1477,6 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp) int i; struct rcu_data *rdp = __this_cpu_ptr(rsp->rda); - /* - * If there is an rcu_barrier() operation in progress, then - * only the task doing that operation is permitted to adopt - * callbacks. To do otherwise breaks rcu_barrier() and friends - * by causing them to fail to wait for the callbacks in the - * orphanage. - */ - if (rsp->rcu_barrier_in_progress && - rsp->rcu_barrier_in_progress != current) - return; - /* Do the accounting first. */ rdp->qlen_lazy += rsp->qlen_lazy; rdp->qlen += rsp->qlen; @@ -1551,9 +1531,8 @@ static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) * The CPU has been completely removed, and some other CPU is reporting * this fact from process context. Do the remainder of the cleanup, * including orphaning the outgoing CPU's RCU callbacks, and also - * adopting them, if there is no _rcu_barrier() instance running. - * There can only be one CPU hotplug operation at a time, so no other - * CPU can be attempting to update rcu_cpu_kthread_task. + * adopting them. There can only be one CPU hotplug operation at a time, + * so no other CPU can be attempting to update rcu_cpu_kthread_task. */ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) { @@ -1611,14 +1590,13 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL, "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n", cpu, rdp->qlen, rdp->nxtlist); + init_callback_list(rdp); + /* Disallow further callbacks on this CPU. */ + rdp->nxttail[RCU_NEXT_TAIL] = NULL; } #else /* #ifdef CONFIG_HOTPLUG_CPU */ -static void rcu_adopt_orphan_cbs(struct rcu_state *rsp) -{ -} - static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) { } @@ -1987,8 +1965,6 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), head->func = func; head->next = NULL; - smp_mb(); /* Ensure RCU update seen before callback registry. */ - /* * Opportunistically note grace-period endings and beginnings. * Note that we might see a beginning right after we see an @@ -1999,6 +1975,12 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), rdp = this_cpu_ptr(rsp->rda); /* Add the callback to our list. */ + if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL)) { + /* _call_rcu() is illegal on offline CPU; leak the callback. */ + WARN_ON_ONCE(1); + local_irq_restore(flags); + return; + } ACCESS_ONCE(rdp->qlen)++; if (lazy) rdp->qlen_lazy++; @@ -2367,13 +2349,10 @@ static void rcu_barrier_func(void *type) static void _rcu_barrier(struct rcu_state *rsp) { int cpu; - unsigned long flags; struct rcu_data *rdp; - struct rcu_data rd; unsigned long snap = ACCESS_ONCE(rsp->n_barrier_done); unsigned long snap_done; - init_rcu_head_on_stack(&rd.barrier_head); _rcu_barrier_trace(rsp, "Begin", -1, snap); /* Take mutex to serialize concurrent rcu_barrier() requests. */ @@ -2413,70 +2392,30 @@ static void _rcu_barrier(struct rcu_state *rsp) /* * Initialize the count to one rather than to zero in order to * avoid a too-soon return to zero in case of a short grace period - * (or preemption of this task). Also flag this task as doing - * an rcu_barrier(). This will prevent anyone else from adopting - * orphaned callbacks, which could cause otherwise failure if a - * CPU went offline and quickly came back online. To see this, - * consider the following sequence of events: - * - * 1. We cause CPU 0 to post an rcu_barrier_callback() callback. - * 2. CPU 1 goes offline, orphaning its callbacks. - * 3. CPU 0 adopts CPU 1's orphaned callbacks. - * 4. CPU 1 comes back online. - * 5. We cause CPU 1 to post an rcu_barrier_callback() callback. - * 6. Both rcu_barrier_callback() callbacks are invoked, awakening - * us -- but before CPU 1's orphaned callbacks are invoked!!! + * (or preemption of this task). Exclude CPU-hotplug operations + * to ensure that no offline CPU has callbacks queued. */ init_completion(&rsp->barrier_completion); atomic_set(&rsp->barrier_cpu_count, 1); - raw_spin_lock_irqsave(&rsp->onofflock, flags); - rsp->rcu_barrier_in_progress = current; - raw_spin_unlock_irqrestore(&rsp->onofflock, flags); + get_online_cpus(); /* - * Force every CPU with callbacks to register a new callback - * that will tell us when all the preceding callbacks have - * been invoked. If an offline CPU has callbacks, wait for - * it to either come back online or to finish orphaning those - * callbacks. + * Force each CPU with callbacks to register a new callback. + * When that callback is invoked, we will know that all of the + * corresponding CPU's preceding callbacks have been invoked. */ - for_each_possible_cpu(cpu) { - preempt_disable(); + for_each_online_cpu(cpu) { rdp = per_cpu_ptr(rsp->rda, cpu); - if (cpu_is_offline(cpu)) { - _rcu_barrier_trace(rsp, "Offline", cpu, - rsp->n_barrier_done); - preempt_enable(); - while (cpu_is_offline(cpu) && ACCESS_ONCE(rdp->qlen)) - schedule_timeout_interruptible(1); - } else if (ACCESS_ONCE(rdp->qlen)) { + if (ACCESS_ONCE(rdp->qlen)) { _rcu_barrier_trace(rsp, "OnlineQ", cpu, rsp->n_barrier_done); smp_call_function_single(cpu, rcu_barrier_func, rsp, 1); - preempt_enable(); } else { _rcu_barrier_trace(rsp, "OnlineNQ", cpu, rsp->n_barrier_done); - preempt_enable(); } } - - /* - * Now that all online CPUs have rcu_barrier_callback() callbacks - * posted, we can adopt all of the orphaned callbacks and place - * an rcu_barrier_callback() callback after them. When that is done, - * we are guaranteed to have an rcu_barrier_callback() callback - * following every callback that could possibly have been - * registered before _rcu_barrier() was called. - */ - raw_spin_lock_irqsave(&rsp->onofflock, flags); - rcu_adopt_orphan_cbs(rsp); - rsp->rcu_barrier_in_progress = NULL; - raw_spin_unlock_irqrestore(&rsp->onofflock, flags); - atomic_inc(&rsp->barrier_cpu_count); - smp_mb__after_atomic_inc(); /* Ensure atomic_inc() before callback. */ - rd.rsp = rsp; - rsp->call(&rd.barrier_head, rcu_barrier_callback); + put_online_cpus(); /* * Now that we have an rcu_barrier_callback() callback on each @@ -2497,8 +2436,6 @@ static void _rcu_barrier(struct rcu_state *rsp) /* Other rcu_barrier() invocations can now safely proceed. */ mutex_unlock(&rsp->barrier_mutex); - - destroy_rcu_head_on_stack(&rd.barrier_head); } /** @@ -2564,6 +2501,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible) rdp->qlen_last_fqs_check = 0; rdp->n_force_qs_snap = rsp->n_force_qs; rdp->blimit = blimit; + init_callback_list(rdp); /* Re-enable callbacks on this CPU. */ rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; atomic_set(&rdp->dynticks->dynticks, (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1); |
