perf_counter: Annotate exit ctx recursion

Ever since Paul fixed it to unclone the context before taking the
ctx->lock this became a false positive, annotate it away.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 12 insertions, 1 deletions

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 51c571ee4d0b..ae591a1275a6 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -3879,7 +3879,18 @@ void perf_counter_exit_task(struct task_struct *child)
         spin_unlock(&child_ctx->lock);
         local_irq_restore(flags);
 
-        mutex_lock(&child_ctx->mutex);
+        /*
+         * We can recurse on the same lock type through:
+         *
+         *   __perf_counter_exit_task()
+         *     sync_child_counter()
+         *       fput(parent_counter->filp)
+         *         perf_release()
+         *           mutex_lock(&ctx->mutex)
+         *
+         * But since its the parent context it won't be the same instance.
+         */
+        mutex_lock_nested(&child_ctx->mutex, SINGLE_DEPTH_NESTING);
 
 again:
         list_for_each_entry_safe(child_counter, tmp, &child_ctx->counter_list,