perf: Fix perf_event_comm() vs. exec() assumption

perf_event_comm() assumes that set_task_comm() is only called on
exec(), and in particular that its only called on current.

Neither are true, as Dave reported a WARN triggered by set_task_comm()
being called on !current.

Separate the exec() hook from the comm hook.

Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/20140521153219.GH5226@laptop.programming.kicks-ass.net
[ Build fix. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 16 insertions, 12 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 440eefc6739..647698f9198 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2970,6 +2970,22 @@ out:
 	local_irq_restore(flags);
 }
 
+void perf_event_exec(void)
+{
+	struct perf_event_context *ctx;
+	int ctxn;
+
+	rcu_read_lock();
+	for_each_task_context_nr(ctxn) {
+		ctx = current->perf_event_ctxp[ctxn];
+		if (!ctx)
+			continue;
+
+		perf_event_enable_on_exec(ctx);
+	}
+	rcu_read_unlock();
+}
+
 /*
  * Cross CPU call to read the hardware event
  */
@@ -5057,18 +5073,6 @@ static void perf_event_comm_event(struct perf_comm_event *comm_event)
 void perf_event_comm(struct task_struct *task)
 {
 	struct perf_comm_event comm_event;
-	struct perf_event_context *ctx;
-	int ctxn;
-
-	rcu_read_lock();
-	for_each_task_context_nr(ctxn) {
-		ctx = task->perf_event_ctxp[ctxn];
-		if (!ctx)
-			continue;
-
-		perf_event_enable_on_exec(ctx);
-	}
-	rcu_read_unlock();
 
 	if (!atomic_read(&nr_comm_events))
 		return;