Commit-ID: a83fe28e2e45392464858a96745db26ac73670c8 Gitweb: http://git.kernel.org/tip/a83fe28e2e45392464858a96745db26ac73670c8 Author: Peter Zijlstra <pet...@infradead.org> AuthorDate: Thu, 29 Jan 2015 14:44:34 +0100 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Wed, 4 Feb 2015 08:07:12 +0100
perf: Fix put_event() ctx lock So what I suspect; but I'm in zombie mode today it seems; is that while I initially thought that it was impossible for ctx to change when refcount dropped to 0, I now suspect its possible. Note that until perf_remove_from_context() the event is still active and visible on the lists. So a concurrent sys_perf_event_open() from another task into this task can race. Reported-by: Vince Weaver <vincent.wea...@maine.edu> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Stephane Eranian <eran...@gmail.com> Cc: mark.rutl...@arm.com Cc: Jiri Olsa <jo...@redhat.com> Cc: Arnaldo Carvalho de Melo <a...@kernel.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Link: http://lkml.kernel.org/r/20150129134434.gb26...@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mi...@kernel.org> --- kernel/events/core.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 142dbabc..f773fa1 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -947,7 +947,8 @@ static void put_ctx(struct perf_event_context *ctx) * perf_event::mmap_mutex * mmap_sem */ -static struct perf_event_context *perf_event_ctx_lock(struct perf_event *event) +static struct perf_event_context * +perf_event_ctx_lock_nested(struct perf_event *event, int nesting) { struct perf_event_context *ctx; @@ -960,7 +961,7 @@ again: } rcu_read_unlock(); - mutex_lock(&ctx->mutex); + mutex_lock_nested(&ctx->mutex, nesting); if (event->ctx != ctx) { mutex_unlock(&ctx->mutex); put_ctx(ctx); @@ -970,6 +971,12 @@ again: return ctx; } +static inline struct perf_event_context * +perf_event_ctx_lock(struct perf_event *event) +{ + return perf_event_ctx_lock_nested(event, 0); +} + static void perf_event_ctx_unlock(struct perf_event *event, struct perf_event_context *ctx) { @@ -3572,7 +3579,7 @@ static void perf_remove_from_owner(struct perf_event *event) */ static void put_event(struct perf_event *event) { - struct perf_event_context *ctx = event->ctx; + struct perf_event_context *ctx; if (!atomic_long_dec_and_test(&event->refcount)) return; @@ -3580,7 +3587,6 @@ static void put_event(struct perf_event *event) if (!is_kernel_event(event)) perf_remove_from_owner(event); - WARN_ON_ONCE(ctx->parent_ctx); /* * There are two ways this annotation is useful: * @@ -3593,7 +3599,8 @@ static void put_event(struct perf_event *event) * the last filedesc died, so there is no possibility * to trigger the AB-BA case. */ - mutex_lock_nested(&ctx->mutex, SINGLE_DEPTH_NESTING); + ctx = perf_event_ctx_lock_nested(event, SINGLE_DEPTH_NESTING); + WARN_ON_ONCE(ctx->parent_ctx); perf_remove_from_context(event, true); mutex_unlock(&ctx->mutex); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
