diff options
Diffstat (limited to 'kernel/smp.c')
| -rw-r--r-- | kernel/smp.c | 108 |
1 files changed, 61 insertions, 47 deletions
diff --git a/kernel/smp.c b/kernel/smp.c index 27dc31a146a3..f349960f79ca 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -86,13 +86,15 @@ int smpcfd_dead_cpu(unsigned int cpu) int smpcfd_dying_cpu(unsigned int cpu) { /* - * The IPIs for the smp-call-function callbacks queued by other - * CPUs might arrive late, either due to hardware latencies or - * because this CPU disabled interrupts (inside stop-machine) - * before the IPIs were sent. So flush out any pending callbacks - * explicitly (without waiting for the IPIs to arrive), to - * ensure that the outgoing CPU doesn't go offline with work - * still pending. + * The IPIs for the smp-call-function callbacks queued by other CPUs + * might arrive late, either due to hardware latencies or because this + * CPU disabled interrupts (inside stop-machine) before the IPIs were + * sent. So flush out any pending callbacks explicitly (without waiting + * for the IPIs to arrive), to ensure that the outgoing CPU doesn't go + * offline with work still pending. + * + * This runs with interrupts disabled inside the stopper task invoked by + * stop_machine(), ensuring mutually exclusive CPU offlining and IPI flush. */ __flush_smp_call_function_queue(false); irq_work_run(); @@ -170,9 +172,9 @@ static DEFINE_PER_CPU(smp_call_func_t, cur_csd_func); static DEFINE_PER_CPU(void *, cur_csd_info); static ulong csd_lock_timeout = 5000; /* CSD lock timeout in milliseconds. */ -module_param(csd_lock_timeout, ulong, 0444); +module_param(csd_lock_timeout, ulong, 0644); static int panic_on_ipistall; /* CSD panic timeout in milliseconds, 300000 for five minutes. */ -module_param(panic_on_ipistall, int, 0444); +module_param(panic_on_ipistall, int, 0644); static atomic_t csd_bug_count = ATOMIC_INIT(0); @@ -418,6 +420,10 @@ void __smp_call_single_queue(int cpu, struct llist_node *node) */ static int generic_exec_single(int cpu, call_single_data_t *csd) { + /* + * Preemption already disabled here so stopper cannot run on this CPU, + * ensuring mutually exclusive CPU offlining and last IPI flush. + */ if (cpu == smp_processor_id()) { smp_call_func_t func = csd->func; void *info = csd->info; @@ -638,8 +644,10 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info, int err; /* - * prevent preemption and reschedule on another processor, - * as well as CPU removal + * Prevent preemption and reschedule on another CPU, as well as CPU + * removal. This prevents stopper from running on this CPU, thus + * providing mutual exclusion of the below cpu_online() check and + * IPI sending ensuring IPI are not missed by CPU going offline. */ this_cpu = get_cpu(); @@ -741,32 +749,19 @@ EXPORT_SYMBOL_GPL(smp_call_function_single_async); * * Selection preference: * 1) current cpu if in @mask - * 2) any cpu of current node if in @mask - * 3) any other online cpu in @mask + * 2) nearest cpu in @mask, based on NUMA topology */ int smp_call_function_any(const struct cpumask *mask, smp_call_func_t func, void *info, int wait) { unsigned int cpu; - const struct cpumask *nodemask; int ret; /* Try for same CPU (cheapest) */ cpu = get_cpu(); - if (cpumask_test_cpu(cpu, mask)) - goto call; - - /* Try for same node. */ - nodemask = cpumask_of_node(cpu_to_node(cpu)); - for (cpu = cpumask_first_and(nodemask, mask); cpu < nr_cpu_ids; - cpu = cpumask_next_and(cpu, nodemask, mask)) { - if (cpu_online(cpu)) - goto call; - } + if (!cpumask_test_cpu(cpu, mask)) + cpu = sched_numa_find_nth_cpu(mask, 0, cpu_to_node(cpu)); - /* Any online will do: smp_call_function_single handles nr_cpu_ids. */ - cpu = cpumask_any_and(mask, cpu_online_mask); -call: ret = smp_call_function_single(cpu, func, info, wait); put_cpu(); return ret; @@ -792,7 +787,6 @@ static void smp_call_function_many_cond(const struct cpumask *mask, bool wait = scf_flags & SCF_WAIT; int nr_cpus = 0; bool run_remote = false; - bool run_local = false; lockdep_assert_preemption_disabled(); @@ -814,18 +808,8 @@ static void smp_call_function_many_cond(const struct cpumask *mask, */ WARN_ON_ONCE(!in_task()); - /* Check if we need local execution. */ - if ((scf_flags & SCF_RUN_LOCAL) && cpumask_test_cpu(this_cpu, mask)) - run_local = true; - /* Check if we need remote execution, i.e., any CPU excluding this one. */ - cpu = cpumask_first_and(mask, cpu_online_mask); - if (cpu == this_cpu) - cpu = cpumask_next_and(cpu, mask, cpu_online_mask); - if (cpu < nr_cpu_ids) - run_remote = true; - - if (run_remote) { + if (cpumask_any_and_but(mask, cpu_online_mask, this_cpu) < nr_cpu_ids) { cfd = this_cpu_ptr(&cfd_data); cpumask_and(cfd->cpumask, mask, cpu_online_mask); __cpumask_clear_cpu(this_cpu, cfd->cpumask); @@ -839,6 +823,9 @@ static void smp_call_function_many_cond(const struct cpumask *mask, continue; } + /* Work is enqueued on a remote CPU. */ + run_remote = true; + csd_lock(csd); if (wait) csd->node.u_flags |= CSD_TYPE_SYNC; @@ -850,6 +837,10 @@ static void smp_call_function_many_cond(const struct cpumask *mask, #endif trace_csd_queue_cpu(cpu, _RET_IP_, func, csd); + /* + * Kick the remote CPU if this is the first work + * item enqueued. + */ if (llist_add(&csd->node.llist, &per_cpu(call_single_queue, cpu))) { __cpumask_set_cpu(cpu, cfd->cpumask_ipi); nr_cpus++; @@ -868,7 +859,9 @@ static void smp_call_function_many_cond(const struct cpumask *mask, send_call_function_ipi_mask(cfd->cpumask_ipi); } - if (run_local && (!cond_func || cond_func(this_cpu, info))) { + /* Check if we need local execution. */ + if ((scf_flags & SCF_RUN_LOCAL) && cpumask_test_cpu(this_cpu, mask) && + (!cond_func || cond_func(this_cpu, info))) { unsigned long flags; local_irq_save(flags); @@ -891,16 +884,15 @@ static void smp_call_function_many_cond(const struct cpumask *mask, * @mask: The set of cpus to run on (only runs on online subset). * @func: The function to run. This must be fast and non-blocking. * @info: An arbitrary pointer to pass to the function. - * @wait: Bitmask that controls the operation. If %SCF_WAIT is set, wait - * (atomically) until function has completed on other CPUs. If - * %SCF_RUN_LOCAL is set, the function will also be run locally - * if the local CPU is set in the @cpumask. - * - * If @wait is true, then returns once @func has returned. + * @wait: If true, wait (atomically) until function has completed + * on other CPUs. * * You must not call this function with disabled interrupts or from a * hardware interrupt handler or from a bottom half handler. Preemption * must be disabled when calling this function. + * + * @func is not called on the local CPU even if @mask contains it. Consider + * using on_each_cpu_cond_mask() instead if this is not desirable. */ void smp_call_function_many(const struct cpumask *mask, smp_call_func_t func, void *info, bool wait) @@ -1025,7 +1017,7 @@ void __init smp_init(void) * @cond_func: A callback function that is passed a cpu id and * the info parameter. The function is called * with preemption disabled. The function should - * return a blooean value indicating whether to IPI + * return a boolean value indicating whether to IPI * the specified CPU. * @func: The function to run on all applicable CPUs. * This must be fast and non-blocking. @@ -1096,6 +1088,28 @@ void wake_up_all_idle_cpus(void) EXPORT_SYMBOL_GPL(wake_up_all_idle_cpus); /** + * cpus_peek_for_pending_ipi - Check for pending IPI for CPUs + * @mask: The CPU mask for the CPUs to check. + * + * This function walks through the @mask to check if there are any pending IPIs + * scheduled, for any of the CPUs in the @mask. It does not guarantee + * correctness as it only provides a racy snapshot. + * + * Returns true if there is a pending IPI scheduled and false otherwise. + */ +bool cpus_peek_for_pending_ipi(const struct cpumask *mask) +{ + unsigned int cpu; + + for_each_cpu(cpu, mask) { + if (!llist_empty(per_cpu_ptr(&call_single_queue, cpu))) + return true; + } + + return false; +} + +/** * struct smp_call_on_cpu_struct - Call a function on a specific CPU * @work: &work_struct * @done: &completion to signal |