linux-kernel - Re: [PATCH] cgroup: freezer: call cgroup_enter_frozen() with preemption disabled in ptrace

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Message-ID: <20191009152136.GA19519@castle.dhcp.thefacebook.com>
Date:   Wed, 9 Oct 2019 15:21:41 +0000
From:   Roman Gushchin <guro@...com>
To:     Oleg Nesterov <oleg@...hat.com>
CC:     Tejun Heo <tj@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Richard Purdie <richard.purdie@...uxfoundation.org>,
        Bruce Ashfield <bruce.ashfield@...il.com>
Subject: Re: [PATCH] cgroup: freezer: call cgroup_enter_frozen() with
 preemption disabled in ptrace_stop()

On Wed, Oct 09, 2019 at 05:02:30PM +0200, Oleg Nesterov wrote:
> ptrace_stop() does preempt_enable_no_resched() to avoid the preemption,
> but after that cgroup_enter_frozen() does spin_lock/unlock and this adds
> another preemption point.
> 
> Reported-and-tested-by: Bruce Ashfield <bruce.ashfield@...il.com>
> Fixes: 76f969e8948d ("cgroup: cgroup v2 freezer")
> Cc: stable@...r.kernel.org # v5.2+
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/signal.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/signal.c b/kernel/signal.c
> index 534fec2..f8eed86 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2205,8 +2205,8 @@ static void ptrace_stop(int exit_code, int why, int clear_code, kernel_siginfo_t
>  		 */
>  		preempt_disable();
>  		read_unlock(&tasklist_lock);
> -		preempt_enable_no_resched();
>  		cgroup_enter_frozen();
> +		preempt_enable_no_resched();

Acked-by: Roman Gushchin <guro@...com>

Thank you!