linux-kernel - [PATCH 05/12] unwind: Add comment to unwind_deferred_task

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Message-ID: <20250924080118.893367437@infradead.org>
Date: Wed, 24 Sep 2025 09:59:53 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: jpoimboe@...nel.org,
 rostedt@...nel.org
Cc: linux-kernel@...r.kernel.org,
 peterz@...radead.org
Subject: [PATCH 05/12] 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@...radead.org>
---
 kernel/exit.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -934,7 +934,6 @@ 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);
 
 	/*
@@ -945,6 +944,12 @@ 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.
+	 */
+	unwind_deferred_task_exit(tsk);
 
 	exit_mm();