linux-kernel - Re: [PATCH 3/7] kernel: stop masking signals in create_io

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Date:   Fri, 26 Mar 2021 15:44:30 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Jens Axboe <axboe@...nel.dk>
Cc:     io-uring@...r.kernel.org, torvalds@...ux-foundation.org,
        metze@...ba.org, oleg@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] kernel: stop masking signals in create_io_thread()

Jens Axboe <axboe@...nel.dk> writes:

> This is racy - move the blocking into when the task is created and
> we're marking it as PF_IO_WORKER anyway. The IO threads are now
> prepared to handle signals like SIGSTOP as well, so clear that from
> the mask to allow proper stopping of IO threads.

Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

>
> Reported-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Jens Axboe <axboe@...nel.dk>
> ---
>  kernel/fork.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index d3171e8e88e5..ddaa15227071 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1940,8 +1940,14 @@ static __latent_entropy struct task_struct *copy_process(
>  	p = dup_task_struct(current, node);
>  	if (!p)
>  		goto fork_out;
> -	if (args->io_thread)
> +	if (args->io_thread) {
> +		/*
> +		 * Mark us an IO worker, and block any signal that isn't
> +		 * fatal or STOP
> +		 */
>  		p->flags |= PF_IO_WORKER;
> +		siginitsetinv(&p->blocked, sigmask(SIGKILL)|sigmask(SIGSTOP));
> +	}
>  
>  	/*
>  	 * This _must_ happen before we call free_task(), i.e. before we jump
> @@ -2430,14 +2436,8 @@ struct task_struct *create_io_thread(int (*fn)(void *), void *arg, int node)
>  		.stack_size	= (unsigned long)arg,
>  		.io_thread	= 1,
>  	};
> -	struct task_struct *tsk;
>  
> -	tsk = copy_process(NULL, 0, node, &args);
> -	if (!IS_ERR(tsk)) {
> -		sigfillset(&tsk->blocked);
> -		sigdelsetmask(&tsk->blocked, sigmask(SIGKILL));
> -	}
> -	return tsk;
> +	return copy_process(NULL, 0, node, &args);
>  }
>  
>  /*