Re: [PATCH] posix-cpu-timers: don't abuse lock_task_sighand() in handle_posix_cpu_timers()

[Frederic Weisbecker <frederic@kernel.org>]

Le Sat, Jul 04, 2026 at 01:09:36PM +0200, Oleg Nesterov a écrit :
> After the commit f90fff1e152d ("posix-cpu-timers: fix race between
> handle_posix_cpu_timers() and posix_cpu_timer_del()"), tsk->sighand
> is stable in handle_posix_cpu_timers(), so it can use the plain
> spin_lock_irqsave(&tsk->sighand->siglock).
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

> ---
>  kernel/time/posix-cpu-timers.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
> index a7d3e8229c4b..d73d31c7994f 100644
> --- a/kernel/time/posix-cpu-timers.c
> +++ b/kernel/time/posix-cpu-timers.c
> @@ -1357,8 +1357,11 @@ static void handle_posix_cpu_timers(struct task_struct *tsk)
>  	unsigned long flags, start;
>  	LIST_HEAD(firing);
>  
> -	if (!lock_task_sighand(tsk, &flags))
> -		return;
> +	/*
> +	 * tsk is current and ->sighand is stable, see the
> +	 * tsk->exit_state check in run_posix_cpu_timers()
> +	 */
> +	spin_lock_irqsave(&tsk->sighand->siglock, flags);
>  
>  	do {
>  		/*
> @@ -1418,7 +1421,7 @@ static void handle_posix_cpu_timers(struct task_struct *tsk)
>  	 * that gets the timer lock before we do will give it up and
>  	 * spin until we've taken care of that timer below.
>  	 */
> -	unlock_task_sighand(tsk, &flags);
> +	spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
>  
>  	/*
>  	 * Now that all the timers on our list have the firing flag,
> -- 
> 2.52.0
> 
> 

-- 
Frederic Weisbecker
SUSE Labs