Commit-ID: a0507c84bf47dfd204299774f45fd16da33f0619 Gitweb: http://git.kernel.org/tip/a0507c84bf47dfd204299774f45fd16da33f0619 Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> AuthorDate: Thu, 6 May 2010 15:42:53 +0200 Committer: Ingo Molnar <mingo@xxxxxxx> CommitDate: Fri, 7 May 2010 11:30:59 +0200 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@xxxxxxxxxx> Cc: Paul Mackerras <paulus@xxxxxxxxx> Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@xxxxxxx> --- 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, -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
|