Re: [RFC PATCH 1/8] signal: Dequeue SIGKILL even if SIGNAL_GROUP_EXIT/group_exec_task is set

From: Oleg Nesterov <oleg@redhat.com>
To: Mike Christie <michael.christie@oracle.com>
Cc: axboe@kernel.dk, brauner@kernel.org, mst@redhat.com,
	linux-kernel@vger.kernel.org, linux@leemhuis.info,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	stefanha@redhat.com, nicolas.dichtel@6wind.com,
	virtualization@lists.linux-foundation.org,
	torvalds@linux-foundation.org
Subject: Re: [RFC PATCH 1/8] signal: Dequeue SIGKILL even if SIGNAL_GROUP_EXIT/group_exec_task is set
Date: Thu, 18 May 2023 18:25:49 +0200	[thread overview]
Message-ID: <20230518162508.GB20779@redhat.com> (raw)
In-Reply-To: <ab7d07ba-5dc3-95c0-aa7c-c2575d03f429@oracle.com>

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.

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