perf: Fix exit() vs PERF_FORMAT_GROUP

Both Stephane and Corey reported that PERF_FORMAT_GROUP didn't work
as expected if the task the counters were attached to quit before
the read() call.

The cause is that we unconditionally destroy the grouping when we
remove counters from their context. Fix this by only doing this when
we free the counter itself.

Reported-by: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Reported-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1273160566.5605.404.camel@twins>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index c8e375440403de53f6deb7be5e5ad3d0b0bb84e6..bf8f3c00329733b55fcad079ec419ba3ec1f2377 100644 (file)
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -522,6 +522,7 @@ struct pmu {
  * enum perf_event_active_state - the states of a event
  */
 enum perf_event_active_state {
+       PERF_EVENT_STATE_FREE           = -3,
        PERF_EVENT_STATE_ERROR          = -2,
        PERF_EVENT_STATE_OFF            = -1,
        PERF_EVENT_STATE_INACTIVE       =  0,

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 3d1552d3c12b0b632964f0f5b053bbe6a03e72e0..f13c3db765f4505dba1381542ea23e3e1d187265 100644 (file)
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -341,6 +341,9 @@ list_del_event(struct perf_event *event, struct perf_event_context *ctx)
        if (event->state > PERF_EVENT_STATE_OFF)
                event->state = PERF_EVENT_STATE_OFF;
 
+       if (event->state > PERF_EVENT_STATE_FREE)
+               return;
+
        /*
         * If this was a group event with sibling events then
         * upgrade the siblings to singleton events by adding them
@@ -1856,6 +1859,8 @@ int perf_event_release_kernel(struct perf_event *event)
 {
        struct perf_event_context *ctx = event->ctx;
 
+       event->state = PERF_EVENT_STATE_FREE;
+
        WARN_ON_ONCE(ctx->parent_ctx);
        mutex_lock(&ctx->mutex);
        perf_event_remove_from_context(event);