perf: Fix exit() vs PERF_FORMAT_GROUP

commit 050735b08ca8a016bbace4445fa025b88fee770b upstream.

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 splitting off
the group destroy from the list removal such that
perf_event_remove_from_context() does not do this and change
perf_event_release() to do so.

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>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1273571513.5605.3527.camel@twins>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 3d1552d3c12b0b632964f0f5b053bbe6a03e72e0..130e0a2f0f04b8e56e47ed64e09e7eef73b9f298 100644 (file)
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -315,8 +315,6 @@ list_add_event(struct perf_event *event, struct perf_event_context *ctx)
 static void
 list_del_event(struct perf_event *event, struct perf_event_context *ctx)
 {
-       struct perf_event *sibling, *tmp;
-
        if (list_empty(&event->group_entry))
                return;
        ctx->nr_events--;
@@ -340,6 +338,12 @@ 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;
+}
+
+static void
+perf_destroy_group(struct perf_event *event, struct perf_event_context *ctx)
+{
+       struct perf_event *sibling, *tmp;
 
        /*
         * If this was a group event with sibling events then
@@ -1856,9 +1860,18 @@ int perf_event_release_kernel(struct perf_event *event)
 {
        struct perf_event_context *ctx = event->ctx;
 
+       /*
+        * Remove from the PMU, can't get re-enabled since we got
+        * here because the last ref went.
+        */
+       perf_event_disable(event);
+
        WARN_ON_ONCE(ctx->parent_ctx);
        mutex_lock(&ctx->mutex);
-       perf_event_remove_from_context(event);
+       raw_spin_lock_irq(&ctx->lock);
+       list_del_event(event, ctx);
+       perf_destroy_group(event, ctx);
+       raw_spin_unlock_irq(&ctx->lock);
        mutex_unlock(&ctx->mutex);
 
        mutex_lock(&event->owner->perf_event_mutex);