On 03/29, Peter Zijlstra wrote:

On Thu, Mar 25, 2021 at 09:14:39AM +0100, Marco Elver wrote:

quoted

@@ -6395,6 +6395,13 @@ static void perf_sigtrap(struct perf_event *event)
 {
 	struct kernel_siginfo info;

+	/*
+	 * This irq_work can race with an exiting task; bail out if sighand has
+	 * already been released in release_task().
+	 */
+	if (!current->sighand)
+		return;

This is racy. If "current" has already passed exit_notify(), current->parent
can do release_task() and destroy current->sighand right after the check.

Urgh.. I'm not entirely sure that check is correct, but I always forget
the rules with signal. It could be we ought to be testing PF_EXISTING
instead.

Agreed, PF_EXISTING check makes more sense in any case, the exiting task
can't receive the signal anyway.

Oleg.