diff options
Diffstat (limited to 'kernel/events')
| -rw-r--r-- | kernel/events/core.c | 31 | ||||
| -rw-r--r-- | kernel/events/ring_buffer.c | 15 |
2 files changed, 36 insertions, 10 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c index 74f22a9..fedba31 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -2497,11 +2497,11 @@ static int __perf_event_stop(void *info) return 0; } -static int perf_event_restart(struct perf_event *event) +static int perf_event_stop(struct perf_event *event, int restart) { struct stop_event_data sd = { .event = event, - .restart = 1, + .restart = restart, }; int ret = 0; @@ -4874,6 +4874,19 @@ static void ring_buffer_attach(struct perf_event *event, spin_unlock_irqrestore(&rb->event_lock, flags); } + /* + * Avoid racing with perf_mmap_close(AUX): stop the event + * before swizzling the event::rb pointer; if it's getting + * unmapped, its aux_mmap_count will be 0 and it won't + * restart. See the comment in __perf_pmu_output_stop(). + * + * Data will inevitably be lost when set_output is done in + * mid-air, but then again, whoever does it like this is + * not in for the data anyway. + */ + if (has_aux(event)) + perf_event_stop(event, 0); + rcu_assign_pointer(event->rb, rb); if (old_rb) { @@ -6150,7 +6163,7 @@ static void perf_event_addr_filters_exec(struct perf_event *event, void *data) raw_spin_unlock_irqrestore(&ifh->lock, flags); if (restart) - perf_event_restart(event); + perf_event_stop(event, 1); } void perf_event_exec(void) @@ -6194,7 +6207,13 @@ static void __perf_event_output_stop(struct perf_event *event, void *data) /* * In case of inheritance, it will be the parent that links to the - * ring-buffer, but it will be the child that's actually using it: + * ring-buffer, but it will be the child that's actually using it. + * + * We are using event::rb to determine if the event should be stopped, + * however this may race with ring_buffer_attach() (through set_output), + * which will make us skip the event that actually needs to be stopped. + * So ring_buffer_attach() has to stop an aux event before re-assigning + * its rb pointer. */ if (rcu_dereference(parent->rb) == rb) ro->err = __perf_event_stop(&sd); @@ -6708,7 +6727,7 @@ static void __perf_addr_filters_adjust(struct perf_event *event, void *data) raw_spin_unlock_irqrestore(&ifh->lock, flags); if (restart) - perf_event_restart(event); + perf_event_stop(event, 1); } /* @@ -7897,7 +7916,7 @@ static void perf_event_addr_filters_apply(struct perf_event *event) mmput(mm); restart: - perf_event_restart(event); + perf_event_stop(event, 1); } /* diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index ae9b90d..257fa46 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -330,15 +330,22 @@ void *perf_aux_output_begin(struct perf_output_handle *handle, if (!rb) return NULL; - if (!rb_has_aux(rb) || !atomic_inc_not_zero(&rb->aux_refcount)) + if (!rb_has_aux(rb)) goto err; /* - * If rb::aux_mmap_count is zero (and rb_has_aux() above went through), - * the aux buffer is in perf_mmap_close(), about to get freed. + * If aux_mmap_count is zero, the aux buffer is in perf_mmap_close(), + * about to get freed, so we leave immediately. + * + * Checking rb::aux_mmap_count and rb::refcount has to be done in + * the same order, see perf_mmap_close. Otherwise we end up freeing + * aux pages in this path, which is a bug, because in_atomic(). */ if (!atomic_read(&rb->aux_mmap_count)) - goto err_put; + goto err; + + if (!atomic_inc_not_zero(&rb->aux_refcount)) + goto err; /* * Nesting is not supported for AUX area, make sure nested |
