perf: Update locking order

Update the locking order to note that ctx::lock nests inside of
child_mutex, as per:

  perf_ioctl():                ctx::mutex
  -> perf_event_for_each():    event::child_mutex
    -> _perf_event_enable():   ctx::lock

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 024adf0..d345964 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1086,8 +1086,8 @@ static void put_ctx(struct perf_event_context *ctx)
  * Lock order:
  *     task_struct::perf_event_mutex
  *       perf_event_context::mutex
- *         perf_event_context::lock
  *         perf_event::child_mutex;
+ *           perf_event_context::lock
  *         perf_event::mmap_mutex
  *         mmap_sem
  */