1 files changed, 91 insertions, 4 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0e8457da6f95..58690af323e4 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)
@@ -2171,9 +2174,10 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx,
          */
         cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);
 
-        perf_event_sched_in(cpuctx, ctx, task);
+        if (ctx->nr_events)
+                cpuctx->task_ctx = ctx;
 
-        cpuctx->task_ctx = ctx;
+        perf_event_sched_in(cpuctx, cpuctx->task_ctx, task);
 
         perf_pmu_enable(ctx->pmu);
         perf_ctx_unlock(cpuctx, ctx);
@@ -3190,12 +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;
@@ -3496,6 +3521,53 @@ 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);
+        if (!rb)
+                goto unlock;
+
+        list_for_each_entry_rcu(event, &rb->event_list, rb_entry)
+                wake_up_all(&event->waitq);
+
+unlock:
+        rcu_read_unlock();
+}
+
 static void rb_free_rcu(struct rcu_head *rcu_head)
 {
         struct ring_buffer *rb;
@@ -3521,9 +3593,19 @@ 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);
 }
 
@@ -3546,6 +3628,7 @@ 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);
@@ -3700,7 +3783,7 @@ 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);
@@ -5822,6 +5905,8 @@ 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);
 
@@ -6028,6 +6113,8 @@ 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);