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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2010-05-06 15:42:53 +0200
committerIngo Molnar <mingo@elte.hu>2010-05-07 11:30:59 +0200
commita0507c84bf47dfd204299774f45fd16da33f0619 (patch)
treed40bf7628ebb9935fb1ef6727337dcd9e2c94fd5 /kernel/perf_event.c
parentcce913178118b0b36742eb7544c2b38a0c957ee7 (diff)
perf: Annotate perf_event_read_group() vs perf_event_release_kernel()
Stephane reported a lockdep warning while using PERF_FORMAT_GROUP. The issue is that perf_event_read_group() takes faults while holding the ctx->mutex, while perf_event_release_kernel() can be called from munmap(). Which makes for an AB-BA deadlock. Except we can never establish the deadlock because we'll only ever call perf_event_release_kernel() after all file descriptors are dead so there is no concurrency possible. Reported-by: Stephane Eranian <eranian@google.com> Cc: Paul Mackerras <paulus@samba.org> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/perf_event.c')
-rw-r--r--kernel/perf_event.c16
1 files changed, 14 insertions, 2 deletions
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 49d8be5a45e3..34659d4085c7 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -1867,7 +1867,19 @@ int perf_event_release_kernel(struct perf_event *event)
event->state = PERF_EVENT_STATE_FREE;
WARN_ON_ONCE(ctx->parent_ctx);
- mutex_lock(&ctx->mutex);
+ /*
+ * There are two ways this annotation is useful:
+ *
+ * 1) there is a lock recursion from perf_event_exit_task
+ * see the comment there.
+ *
+ * 2) there is a lock-inversion with mmap_sem through
+ * perf_event_read_group(), which takes faults while
+ * holding ctx->mutex, however this is called after
+ * the last filedesc died, so there is no possibility
+ * to trigger the AB-BA case.
+ */
+ mutex_lock_nested(&ctx->mutex, SINGLE_DEPTH_NESTING);
perf_event_remove_from_context(event);
mutex_unlock(&ctx->mutex);
@@ -5305,7 +5317,7 @@ void perf_event_exit_task(struct task_struct *child)
*
* But since its the parent context it won't be the same instance.
*/
- mutex_lock_nested(&child_ctx->mutex, SINGLE_DEPTH_NESTING);
+ mutex_lock(&child_ctx->mutex);
again:
list_for_each_entry_safe(child_event, tmp, &child_ctx->pinned_groups,