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

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Message-ID: <20251001113505.25281444@gandalf.local.home>
Date: Wed, 1 Oct 2025 11:35:05 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: jpoimboe@...nel.org, rostedt@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/12] unwind: Add comment to
 unwind_deferred_task_exit()

On Wed, 24 Sep 2025 09:59:53 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> 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.


I would state that it also flushes any unwind that is currently pending, as
exit_mm() will prevent it from happening.

-- Steve


> +	 */
> +	unwind_deferred_task_exit(tsk);
>  
>  	exit_mm();
>  
>