linux-kernel - Re: [PATCH 2/7] io_uring: handle signals for IO threads like a normal thread

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Message-ID: <m1wntty7yn.fsf@fess.ebiederm.org>
Date:   Fri, 26 Mar 2021 15:29:36 -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 2/7] io_uring: handle signals for IO threads like a normal thread

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

> We go through various hoops to disallow signals for the IO threads, but
> there's really no reason why we cannot just allow them. The IO threads
> never return to userspace like a normal thread, and hence don't go through
> normal signal processing. Instead, just check for a pending signal as part
> of the work loop, and call get_signal() to handle it for us if anything
> is pending.
>
> With that, we can support receiving signals, including special ones like
> SIGSTOP.
>
> Signed-off-by: Jens Axboe <axboe@...nel.dk>
> ---
>  fs/io-wq.c    | 24 +++++++++++++++++-------
>  fs/io_uring.c | 12 ++++++++----
>  2 files changed, 25 insertions(+), 11 deletions(-)
>
> diff --git a/fs/io-wq.c b/fs/io-wq.c
> index b7c1fa932cb3..3e2f059a1737 100644
> --- a/fs/io-wq.c
> +++ b/fs/io-wq.c
> @@ -16,7 +16,6 @@
>  #include <linux/rculist_nulls.h>
>  #include <linux/cpu.h>
>  #include <linux/tracehook.h>
> -#include <linux/freezer.h>
>  
>  #include "../kernel/sched/sched.h"
>  #include "io-wq.h"
> @@ -503,10 +502,16 @@ static int io_wqe_worker(void *data)
>  		if (io_flush_signals())
>  			continue;
>  		ret = schedule_timeout(WORKER_IDLE_TIMEOUT);
> -		if (try_to_freeze() || ret)
> +		if (signal_pending(current)) {
> +			struct ksignal ksig;
> +
> +			if (fatal_signal_pending(current))
> +				break;
> +			if (get_signal(&ksig))
> +				continue;
                        ^^^^^^^^^^^^^^^^^^^^^^

That is wrong.  You are promising to deliver a signal to signal
handler and them simply discarding it.  Perhaps:

			if (!get_signal(&ksig))
                        	continue;
			WARN_ON(!sig_kernel_stop(ksig->sig));
                        break;


Eric