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author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2010-05-06 13:42:53 (GMT) |
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committer | Ingo Molnar <mingo@elte.hu> | 2010-05-07 09:30:59 (GMT) |
commit | a0507c84bf47dfd204299774f45fd16da33f0619 (patch) | |
tree | d40bf7628ebb9935fb1ef6727337dcd9e2c94fd5 /kernel/perf_event.c | |
parent | cce913178118b0b36742eb7544c2b38a0c957ee7 (diff) | |
download | linux-a0507c84bf47dfd204299774f45fd16da33f0619.tar.xz |
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.c | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/kernel/perf_event.c b/kernel/perf_event.c index 49d8be5..34659d4 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, |