linux-kernel - Re: [PATCH 1/7] kernel: don't call do_exit() for PF_IO

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Message-ID: <m14kgxy7b4.fsf@fess.ebiederm.org>
Date:   Fri, 26 Mar 2021 15:43:43 -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 1/7] kernel: don't call do_exit() for PF_IO_WORKER threads

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

> Right now we're never calling get_signal() from PF_IO_WORKER threads, but
> in preparation for doing so, don't handle a fatal signal for them. The
> workers have state they need to cleanup when exiting, and they don't do
> coredumps, so just return instead of performing either a dump or calling
> do_exit() on their behalf. The threads themselves will detect a fatal
> signal and do proper shutdown.
>
> Signed-off-by: Jens Axboe <axboe@...nel.dk>
> ---
>  kernel/signal.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/kernel/signal.c b/kernel/signal.c
> index f2a1b898da29..e3e1b8fbfe8a 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2756,6 +2756,15 @@ bool get_signal(struct ksignal *ksig)
>  		 */
>  		current->flags |= PF_SIGNALED;
>  
> +		/*
> +		 * PF_IO_WORKER threads will catch and exit on fatal signals
> +		 * themselves. They have cleanup that must be performed, so
> +		 * we cannot call do_exit() on their behalf. coredumps also
> +		 * do not apply to them.
> +		 */
> +		if (current->flags & PF_IO_WORKER)
> +			return false;
> +

Returning false when get_signal needs the caller to handle a signal
adds a very weird and awkward special case to how get_signal returns
arguments.

Instead you should simply break and let get_signal return SIGKILL like
any other signal that has a handler that the caller of get_signal needs
to handle.

Something like:
> +		/*
> +		 * PF_IO_WORKER have cleanup that must be performed,
> +		 * before calling do_exit().
> +		 */
> +		if (current->flags & PF_IO_WORKER)
> +			break;


As do_coredump does not call do_exit there is no reason to skip calling into
the coredump handling either.   And allowing it will remove yet another
special case from the io worker code.

>  		if (sig_kernel_coredump(signr)) {
>  			if (print_fatal_signals)
>  				print_fatal_signal(ksig->info.si_signo);

Eric