]> git.openfabrics.org - ~shefty/rdma-dev.git/blobdiff - kernel/events/core.c
Merge branch 'perf/urgent' into perf/core
[~shefty/rdma-dev.git] / kernel / events / core.c
index 924338bb489ce1f43a400e75a2c5f5df94491cb4..a355ffb0b28f8974c42fb3797b706da040a43789 100644 (file)
@@ -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)
@@ -2175,7 +2178,8 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx,
 
        perf_event_sched_in(cpuctx, ctx, task);
 
-       cpuctx->task_ctx = ctx;
+       if (ctx->nr_events)
+               cpuctx->task_ctx = ctx;
 
        perf_pmu_enable(ctx->pmu);
        perf_ctx_unlock(cpuctx, ctx);
@@ -2983,12 +2987,33 @@ 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;
@@ -3289,6 +3314,49 @@ 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;
@@ -3314,9 +3382,19 @@ 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);
 }
 
@@ -3339,6 +3417,7 @@ 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);
@@ -3493,7 +3572,7 @@ 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);
@@ -5620,6 +5699,8 @@ 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);
 
@@ -5826,6 +5907,8 @@ 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);