From: Peter Zijlstra <peterz@infradead.org>
Date: Mon, 22 Sep 2025 13:46:27 +0000 (+0200)
Subject: unwind: Add comment to unwind_deferred_task_exit()
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=ae577ea0bc5249c483da09670f784dbc288c80b6;p=thirdparty%2Fkernel%2Flinux.git

unwind: Add comment to unwind_deferred_task_exit()

Explain why unwind_deferred_task_exit() exist and its constraints.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://patch.msgid.link/20250924080118.893367437@infradead.org
---

diff --git a/kernel/exit.c b/kernel/exit.c
index 9f74e8f1c431b..5f6e78e28e8a7 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -939,7 +939,6 @@ void __noreturn do_exit(long code)
 
 	tsk->exit_code = code;
 	taskstats_exit(tsk, group_dead);
-	unwind_deferred_task_exit(tsk);
 	trace_sched_process_exit(tsk, group_dead);
 
 	/*
@@ -950,6 +949,12 @@ void __noreturn do_exit(long code)
 	 * gets woken up by child-exit notifications.
 	 */
 	perf_event_exit_task(tsk);
+	/*
+	 * PF_EXITING (above) ensures unwind_deferred_request() will no
+	 * longer add new unwinds. While exit_mm() (below) will destroy the
+	 * abaility to do unwinds. So flush any pending unwinds here.
+	 */
+	unwind_deferred_task_exit(tsk);
 
 	exit_mm();