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Subject: Re: [PATCH] signals: work around random wakeups in sigsuspend()
To: Peter Zijlstra <peterz@infradead.org>, Oleg Nesterov <oleg@redhat.com>
References: <1453735306-13519-1-git-send-email-sasha.levin@oracle.com>
 <20160125133205.36542c86ada93761d8a9ff06@linux-foundation.org>
 <20160126211009.GA4695@redhat.com>
 <20160127084443.GL6357@twins.programming.kicks-ass.net>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
        mingo@kernel.org
From: Sasha Levin <sasha.levin@oracle.com>
Message-ID: <56A8FD4F.5080708@oracle.com>
Date: Wed, 27 Jan 2016 12:24:31 -0500
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On 01/27/2016 03:44 AM, Peter Zijlstra wrote:
> 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);

Should that be the case for sys_pause() too?


Thanks,
Sasha