linux-kernel - [tip: perf/core] unwind: Add comment to unwind_deferred_task

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Message-ID: <176173057815.2601451.5401446227501331662.tip-bot2@tip-bot2>
Date: Wed, 29 Oct 2025 09:36:18 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 "Steven Rostedt (Google)" <rostedt@...dmis.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: perf/core] unwind: Add comment to unwind_deferred_task_exit()

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     ae577ea0bc5249c483da09670f784dbc288c80b6
Gitweb:        https://git.kernel.org/tip/ae577ea0bc5249c483da09670f784dbc288c80b6
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Mon, 22 Sep 2025 15:46:27 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 29 Oct 2025 10:29:55 +01:00

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>
Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>
Link: https://patch.msgid.link/20250924080118.893367437@infradead.org
---
 kernel/exit.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 9f74e8f..5f6e78e 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();