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From: Thomas Gleixner <tglx@kernel.org>
To: Hyunwoo Kim <imv4bel@gmail.com>, Frederic Weisbecker
 <frederic@kernel.org>, Anna-Maria Behnsen <anna-maria@linutronix.de>, Kees
 Cook <kees@kernel.org>, Christian Brauner <brauner@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Oleg Nesterov <oleg@redhat.com>,
 John Stultz <jstultz@google.com>, Ingo Molnar <mingo@kernel.org>,
 Alexander Viro <viro@zeniv.linux.org.uk>, Jan Kara <jack@suse.cz>, "Eric
 W. Biederman" <ebiederm@xmission.com>, linux-kernel@vger.kernel.org,
 linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Hyunwoo Kim
 <imv4bel@gmail.com>
Subject: Re: [PATCH v2] posix-cpu-timers: Dequeue per-thread timers before
 exchange_tids()
In-Reply-To: <ao7Q8miiuLAPVnWv@v4bel>
References: <ao7Q8miiuLAPVnWv@v4bel>
Date: Mon, 31 Aug 2026 13:56:07 +0200
Message-ID: <87bjaicxm0.ffs@fw13>
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On Wed, Aug 26 2026 at 20:41, Hyunwoo Kim wrote:
> diff --git a/fs/exec.c b/fs/exec.c
> index 745f6eb5279e6..9b2d140bd9f2a 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1003,6 +1003,18 @@ static int de_thread(struct task_struct *tsk)
>  		 * the former thread group leader:
>  		 */
>  
> +#ifdef CONFIG_POSIX_TIMERS
> +		/*
> +		 * exchange_tids() hands this thread's PID to the old leader,
> +		 * which is reaped right after. The PID lookup in
> +		 * timer_lock_sighand() then fails while the per thread CPU
> +		 * timers are still queued here, so dequeue them first.
> +		 */
> +		spin_lock(lock);
> +		posix_cpu_timers_exit(tsk);
> +		spin_unlock(lock);
> +#endif
> +
>  		/* Become a process group leader with the old leader's pid.
>  		 * The old leader becomes a thread of the this thread group.
>  		 */

Similar to the other issue vs. POSIX timer signals this really wants to
be solved in exit() independent of non-leader exec(). Let me have a
look.