diff options
| -rw-r--r-- | include/linux/perf_event.h | 1 | ||||
| -rw-r--r-- | kernel/events/core.c | 86 | ||||
| -rw-r--r-- | kernel/events/internal.h | 3 | ||||
| -rw-r--r-- | kernel/events/ring_buffer.c | 3 |
4 files changed, 91 insertions, 2 deletions
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 1e9ebe5e0091..b1f89122bf6a 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -822,6 +822,7 @@ struct perf_event { int mmap_locked; struct user_struct *mmap_user; struct ring_buffer *rb; + struct list_head rb_entry; /* poll related */ wait_queue_head_t waitq; diff --git a/kernel/events/core.c b/kernel/events/core.c index b0c1186fd97b..600c1629b64d 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -185,6 +185,9 @@ static void cpu_ctx_sched_in(struct perf_cpu_context *cpuctx, static void update_context_time(struct perf_event_context *ctx); static u64 perf_event_time(struct perf_event *event); +static void ring_buffer_attach(struct perf_event *event, + struct ring_buffer *rb); + void __weak perf_event_print_debug(void) { } extern __weak const char *perf_pmu_name(void) @@ -3191,12 +3194,33 @@ static unsigned int perf_poll(struct file *file, poll_table *wait) struct ring_buffer *rb; unsigned int events = POLL_HUP; + /* + * Race between perf_event_set_output() and perf_poll(): perf_poll() + * grabs the rb reference but perf_event_set_output() overrides it. + * Here is the timeline for two threads T1, T2: + * t0: T1, rb = rcu_dereference(event->rb) + * t1: T2, old_rb = event->rb + * t2: T2, event->rb = new rb + * t3: T2, ring_buffer_detach(old_rb) + * t4: T1, ring_buffer_attach(rb1) + * t5: T1, poll_wait(event->waitq) + * + * To avoid this problem, we grab mmap_mutex in perf_poll() + * thereby ensuring that the assignment of the new ring buffer + * and the detachment of the old buffer appear atomic to perf_poll() + */ + mutex_lock(&event->mmap_mutex); + rcu_read_lock(); rb = rcu_dereference(event->rb); - if (rb) + if (rb) { + ring_buffer_attach(event, rb); events = atomic_xchg(&rb->poll, 0); + } rcu_read_unlock(); + mutex_unlock(&event->mmap_mutex); + poll_wait(file, &event->waitq, wait); return events; @@ -3497,6 +3521,49 @@ unlock: return ret; } +static void ring_buffer_attach(struct perf_event *event, + struct ring_buffer *rb) +{ + unsigned long flags; + + if (!list_empty(&event->rb_entry)) + return; + + spin_lock_irqsave(&rb->event_lock, flags); + if (!list_empty(&event->rb_entry)) + goto unlock; + + list_add(&event->rb_entry, &rb->event_list); +unlock: + spin_unlock_irqrestore(&rb->event_lock, flags); +} + +static void ring_buffer_detach(struct perf_event *event, + struct ring_buffer *rb) +{ + unsigned long flags; + + if (list_empty(&event->rb_entry)) + return; + + spin_lock_irqsave(&rb->event_lock, flags); + list_del_init(&event->rb_entry); + wake_up_all(&event->waitq); + spin_unlock_irqrestore(&rb->event_lock, flags); +} + +static void ring_buffer_wakeup(struct perf_event *event) +{ + struct ring_buffer *rb; + + rcu_read_lock(); + rb = rcu_dereference(event->rb); + list_for_each_entry_rcu(event, &rb->event_list, rb_entry) { + wake_up_all(&event->waitq); + } + rcu_read_unlock(); +} + static void rb_free_rcu(struct rcu_head *rcu_head) { struct ring_buffer *rb; @@ -3522,9 +3589,19 @@ static struct ring_buffer *ring_buffer_get(struct perf_event *event) static void ring_buffer_put(struct ring_buffer *rb) { + struct perf_event *event, *n; + unsigned long flags; + if (!atomic_dec_and_test(&rb->refcount)) return; + spin_lock_irqsave(&rb->event_lock, flags); + list_for_each_entry_safe(event, n, &rb->event_list, rb_entry) { + list_del_init(&event->rb_entry); + wake_up_all(&event->waitq); + } + spin_unlock_irqrestore(&rb->event_lock, flags); + call_rcu(&rb->rcu_head, rb_free_rcu); } @@ -3547,6 +3624,7 @@ static void perf_mmap_close(struct vm_area_struct *vma) atomic_long_sub((size >> PAGE_SHIFT) + 1, &user->locked_vm); vma->vm_mm->pinned_vm -= event->mmap_locked; rcu_assign_pointer(event->rb, NULL); + ring_buffer_detach(event, rb); mutex_unlock(&event->mmap_mutex); ring_buffer_put(rb); @@ -3701,7 +3779,7 @@ static const struct file_operations perf_fops = { void perf_event_wakeup(struct perf_event *event) { - wake_up_all(&event->waitq); + ring_buffer_wakeup(event); if (event->pending_kill) { kill_fasync(&event->fasync, SIGIO, event->pending_kill); @@ -5823,6 +5901,8 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu, INIT_LIST_HEAD(&event->group_entry); INIT_LIST_HEAD(&event->event_entry); INIT_LIST_HEAD(&event->sibling_list); + INIT_LIST_HEAD(&event->rb_entry); + init_waitqueue_head(&event->waitq); init_irq_work(&event->pending, perf_pending_event); @@ -6029,6 +6109,8 @@ set: old_rb = event->rb; rcu_assign_pointer(event->rb, rb); + if (old_rb) + ring_buffer_detach(event, old_rb); ret = 0; unlock: mutex_unlock(&event->mmap_mutex); diff --git a/kernel/events/internal.h b/kernel/events/internal.h index 09097dd8116c..64568a699375 100644 --- a/kernel/events/internal.h +++ b/kernel/events/internal.h @@ -22,6 +22,9 @@ struct ring_buffer { local_t lost; /* nr records lost */ long watermark; /* wakeup watermark */ + /* poll crap */ + spinlock_t event_lock; + struct list_head event_list; struct perf_event_mmap_page *user_page; void *data_pages[0]; diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index a2a29205cc0f..7f3011c6b57f 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -209,6 +209,9 @@ ring_buffer_init(struct ring_buffer *rb, long watermark, int flags) rb->writable = 1; atomic_set(&rb->refcount, 1); + + INIT_LIST_HEAD(&rb->event_list); + spin_lock_init(&rb->event_lock); } #ifndef CONFIG_PERF_USE_VMALLOC |