linux-kernel - Re: [PATCH] signals: work around random wakeups in sigsuspend()

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Message-ID: <20160127084443.GL6357@twins.programming.kicks-ass.net>
Date:	Wed, 27 Jan 2016 09:44:43 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org, mingo@...nel.org
Subject: Re: [PATCH] signals: work around random wakeups in sigsuspend()

On Tue, Jan 26, 2016 at 10:10:09PM +0100, Oleg Nesterov wrote:

> And, ironically, there is another more serious "reverse" problem ;) sigsuspend()
> orany other user of -ERESTARTNOHAND can "miss" the signal, in a sense that the
> kernel can wrongly restart this syscall after return from signal handler. This
> is not trivial to fix..

So I'm not entirely sure I get what you mean there. But it did get me to
look at the patch again:

+       while (!signal_pending(current)) {
+               __set_current_state(TASK_INTERRUPTIBLE);
+               schedule();
+       }

That should very much be:

	for (;;) {
		set_current_state(TASK_INTERRUPTIBLE);
		if (signal_pending(current))
			break;
		schedule();
	}
	__set_current_state(TASK_RUNNING);