Re: [PATCH v2] posix-cpu-timers: Dequeue per-thread timers before exchange_tids()

[Thomas Gleixner <tglx@kernel.org>]

On Mon, Aug 31 2026 at 13:56, Thomas Gleixner wrote:
> 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.

Duh. That's about the non-leader itself....

Why did anyone think that swapping TIDs is a brilliant idea?

I still think that this should be done differently. There is no point in
doing the disarming in release_task(). Let me think some more.