linux-kernel - Re: [RFC PATCH 1/8] signal: Dequeue SIGKILL even if SIGNAL_GROUP_EXIT/group_exec

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Date:   Thu, 18 May 2023 18:25:49 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Mike Christie <michael.christie@...cle.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>, linux@...mhuis.info,
        nicolas.dichtel@...nd.com, axboe@...nel.dk,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, mst@...hat.com,
        sgarzare@...hat.com, jasowang@...hat.com, stefanha@...hat.com,
        brauner@...nel.org
Subject: Re: [RFC PATCH 1/8] signal: Dequeue SIGKILL even if
 SIGNAL_GROUP_EXIT/group_exec_task is set

I too do not understand the 1st change in this patch ...

On 05/18, Mike Christie wrote:
>
> In the other patches we do:
>
> if (get_signal(ksig))
> 	start_exit_cleanup_by_stopping_newIO()
> 	flush running IO()
> 	exit()
>
> But to do the flush running IO() part of this I need to wait for it so
> that's why I wanted to be able to dequeue the SIGKILL and clear the
> TIF_SIGPENDING bit.

But get_signal() will do what you need, dequeue SIGKILL and clear SIGPENDING ?

	if ((signal->flags & SIGNAL_GROUP_EXIT) ||
	     signal->group_exec_task) {
		clear_siginfo(&ksig->info);
		ksig->info.si_signo = signr = SIGKILL;
		sigdelset(&current->pending.signal, SIGKILL);

this "dequeues" SIGKILL,

		trace_signal_deliver(SIGKILL, SEND_SIG_NOINFO,
			&sighand->action[SIGKILL - 1]);
		recalc_sigpending();

this clears TIF_SIGPENDING.

> Or I don't need this specifically. In patch 0/8 I said I knew you guys
> would not like it :) If I just have a:
>
> if (fatal_signal())
> 	clear_fatal_signal()

see above...


Well... I think this code is actually wrong if if SIGSTOP is pending and
the task is PF_IO_WORKER, but this is also true for io-threads so we can
discuss this separately.

Oleg.