linux-kernel - Re: [PATCH 5.10 65/73] exit: wait_task_zombie: kill the no longer necessary spin_lock

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Message-ID: <20240313170324.GC25452@redhat.com>
Date: Wed, 13 Mar 2024 18:03:24 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Sasha Levin <sashal@...nel.org>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Dylan Hatch <dylanbhatch@...gle.com>,
	"Eric W . Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 5.10 65/73] exit: wait_task_zombie: kill the no longer
 necessary spin_lock_irq(siglock)

I do not know what does 5.10 mean. Does this tree has all the changes
this patch depends on? Say, 1df4bd83cdfdbd0720dd ("do_io_accounting:
use sig->stats_lock") ?

In any case please remove this patch from all your queues, it got the
"stable" tag by mistake.

Oleg.

On 03/13, Sasha Levin wrote:
>
> From: Oleg Nesterov <oleg@...hat.com>
> 
> [ Upstream commit c1be35a16b2f1fe21f4f26f9de030ad6eaaf6a25 ]
> 
> After the recent changes nobody use siglock to read the values protected
> by stats_lock, we can kill spin_lock_irq(&current->sighand->siglock) and
> update the comment.
> 
> With this patch only __exit_signal() and thread_group_start_cputime() take
> stats_lock under siglock.
> 
> Link: https://lkml.kernel.org/r/20240123153359.GA21866@redhat.com
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Dylan Hatch <dylanbhatch@...gle.com>
> Cc: Eric W. Biederman <ebiederm@...ssion.com>
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  kernel/exit.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/exit.c b/kernel/exit.c
> index c41bdc0a7f06b..8f25abdd5fa7d 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -1106,17 +1106,14 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
>  		 * and nobody can change them.
>  		 *
>  		 * psig->stats_lock also protects us from our sub-threads
> -		 * which can reap other children at the same time. Until
> -		 * we change k_getrusage()-like users to rely on this lock
> -		 * we have to take ->siglock as well.
> +		 * which can reap other children at the same time.
>  		 *
>  		 * We use thread_group_cputime_adjusted() to get times for
>  		 * the thread group, which consolidates times for all threads
>  		 * in the group including the group leader.
>  		 */
>  		thread_group_cputime_adjusted(p, &tgutime, &tgstime);
> -		spin_lock_irq(&current->sighand->siglock);
> -		write_seqlock(&psig->stats_lock);
> +		write_seqlock_irq(&psig->stats_lock);
>  		psig->cutime += tgutime + sig->cutime;
>  		psig->cstime += tgstime + sig->cstime;
>  		psig->cgtime += task_gtime(p) + sig->gtime + sig->cgtime;
> @@ -1139,8 +1136,7 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
>  			psig->cmaxrss = maxrss;
>  		task_io_accounting_add(&psig->ioac, &p->ioac);
>  		task_io_accounting_add(&psig->ioac, &sig->ioac);
> -		write_sequnlock(&psig->stats_lock);
> -		spin_unlock_irq(&current->sighand->siglock);
> +		write_sequnlock_irq(&psig->stats_lock);
>  	}
>  
>  	if (wo->wo_rusage)
> -- 
> 2.43.0
>