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Subject: Re: [PATCH AUTOSEL 5.11 43/44] signal: don't allow STOP on
 PF_IO_WORKER threads
To:     Sasha Levin <sashal@kernel.org>, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        Jens Axboe <axboe@kernel.dk>
References: <20210325112459.1926846-1-sashal@kernel.org>
 <20210325112459.1926846-43-sashal@kernel.org>
From:   Stefan Metzmacher <metze@samba.org>
Message-ID: <f4c932b4-b787-651e-dd9f-584b386acddb@samba.org>
Date:   Thu, 25 Mar 2021 12:34:18 +0100
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Am 25.03.21 um 12:24 schrieb Sasha Levin:
> From: "Eric W. Biederman" <ebiederm@xmission.com>
> 
> [ Upstream commit 4db4b1a0d1779dc159f7b87feb97030ec0b12597 ]
> 
> Just like we don't allow normal signals to IO threads, don't deliver a
> STOP to a task that has PF_IO_WORKER set. The IO threads don't take
> signals in general, and have no means of flushing out a stop either.
> 
> Longer term, we may want to look into allowing stop of these threads,
> as it relates to eg process freezing. For now, this prevents a spin
> issue if a SIGSTOP is delivered to the parent task.
> 
> Reported-by: Stefan Metzmacher <metze@samba.org>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  kernel/signal.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/signal.c b/kernel/signal.c
> index 55526b941011..00a3840f6037 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -288,7 +288,8 @@ bool task_set_jobctl_pending(struct task_struct *task, unsigned long mask)
>  			JOBCTL_STOP_SIGMASK | JOBCTL_TRAPPING));
>  	BUG_ON((mask & JOBCTL_TRAPPING) && !(mask & JOBCTL_PENDING_MASK));
>  
> -	if (unlikely(fatal_signal_pending(task) || (task->flags & PF_EXITING)))
> +	if (unlikely(fatal_signal_pending(task) ||
> +		     (task->flags & (PF_EXITING | PF_IO_WORKER))))
>  		return false;
>  
>  	if (mask & JOBCTL_STOP_SIGMASK)
> 

Again, why is this proposed for 5.11 and 5.10 already?

metze