diff options
Diffstat (limited to 'kernel/smp.c')
| -rw-r--r-- | kernel/smp.c | 71 |
1 files changed, 52 insertions, 19 deletions
diff --git a/kernel/smp.c b/kernel/smp.c index 9910744f0856..7cbd0f293df4 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -194,7 +194,7 @@ void generic_smp_call_function_interrupt(void) */ list_for_each_entry_rcu(data, &call_function.queue, csd.list) { int refs; - void (*func) (void *info); + smp_call_func_t func; /* * Since we walk the list without any locks, we might @@ -214,17 +214,17 @@ void generic_smp_call_function_interrupt(void) if (atomic_read(&data->refs) == 0) continue; - func = data->csd.func; /* for later warn */ - data->csd.func(data->csd.info); + func = data->csd.func; /* save for later warn */ + func(data->csd.info); /* - * If the cpu mask is not still set then it enabled interrupts, - * we took another smp interrupt, and executed the function - * twice on this cpu. In theory that copy decremented refs. + * If the cpu mask is not still set then func enabled + * interrupts (BUG), and this cpu took another smp call + * function interrupt and executed func(info) twice + * on this cpu. That nested execution decremented refs. */ if (!cpumask_test_and_clear_cpu(cpu, data->cpumask)) { - WARN(1, "%pS enabled interrupts and double executed\n", - func); + WARN(1, "%pf enabled interrupts and double executed\n", func); continue; } @@ -450,7 +450,7 @@ void smp_call_function_many(const struct cpumask *mask, { struct call_function_data *data; unsigned long flags; - int cpu, next_cpu, this_cpu = smp_processor_id(); + int refs, cpu, next_cpu, this_cpu = smp_processor_id(); /* * Can deadlock when called with interrupts disabled. @@ -461,7 +461,7 @@ void smp_call_function_many(const struct cpumask *mask, WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled() && !oops_in_progress && !early_boot_irqs_disabled); - /* So, what's a CPU they want? Ignoring this one. */ + /* Try to fastpath. So, what's a CPU they want? Ignoring this one. */ cpu = cpumask_first_and(mask, cpu_online_mask); if (cpu == this_cpu) cpu = cpumask_next_and(cpu, mask, cpu_online_mask); @@ -483,22 +483,49 @@ void smp_call_function_many(const struct cpumask *mask, data = &__get_cpu_var(cfd_data); csd_lock(&data->csd); + + /* This BUG_ON verifies our reuse assertions and can be removed */ BUG_ON(atomic_read(&data->refs) || !cpumask_empty(data->cpumask)); + /* + * The global call function queue list add and delete are protected + * by a lock, but the list is traversed without any lock, relying + * on the rcu list add and delete to allow safe concurrent traversal. + * We reuse the call function data without waiting for any grace + * period after some other cpu removes it from the global queue. + * This means a cpu might find our data block as it is being + * filled out. + * + * We hold off the interrupt handler on the other cpu by + * ordering our writes to the cpu mask vs our setting of the + * refs counter. We assert only the cpu owning the data block + * will set a bit in cpumask, and each bit will only be cleared + * by the subject cpu. Each cpu must first find its bit is + * set and then check that refs is set indicating the element is + * ready to be processed, otherwise it must skip the entry. + * + * On the previous iteration refs was set to 0 by another cpu. + * To avoid the use of transitivity, set the counter to 0 here + * so the wmb will pair with the rmb in the interrupt handler. + */ + atomic_set(&data->refs, 0); /* convert 3rd to 1st party write */ + data->csd.func = func; data->csd.info = info; - cpumask_and(data->cpumask, mask, cpu_online_mask); - cpumask_clear_cpu(this_cpu, data->cpumask); - /* - * To ensure the interrupt handler gets an complete view - * we order the cpumask and refs writes and order the read - * of them in the interrupt handler. In addition we may - * only clear our own cpu bit from the mask. - */ + /* Ensure 0 refs is visible before mask. Also orders func and info */ smp_wmb(); - atomic_set(&data->refs, cpumask_weight(data->cpumask)); + /* We rely on the "and" being processed before the store */ + cpumask_and(data->cpumask, mask, cpu_online_mask); + cpumask_clear_cpu(this_cpu, data->cpumask); + refs = cpumask_weight(data->cpumask); + + /* Some callers race with other cpus changing the passed mask */ + if (unlikely(!refs)) { + csd_unlock(&data->csd); + return; + } raw_spin_lock_irqsave(&call_function.lock, flags); /* @@ -507,6 +534,12 @@ void smp_call_function_many(const struct cpumask *mask, * will not miss any other list entries: */ list_add_rcu(&data->csd.list, &call_function.queue); + /* + * We rely on the wmb() in list_add_rcu to complete our writes + * to the cpumask before this write to refs, which indicates + * data is on the list and is ready to be processed. + */ + atomic_set(&data->refs, refs); raw_spin_unlock_irqrestore(&call_function.lock, flags); /* |