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Date: Tue, 01 Mar 2016 15:44:58 +0100
Message-ID: <s5ha8miuuj9.wl-tiwai@suse.de>
From: Takashi Iwai <tiwai@suse.de>
To: "Dmitry Vyukov" <dvyukov@google.com>
Cc: <alsa-devel@alsa-project.org>, "Jaroslav Kysela" <perex@perex.cz>,
        "LKML" <linux-kernel@vger.kernel.org>,
        "Alexander Potapenko" <glider@google.com>,
        "Kostya Serebryany" <kcc@google.com>,
        "syzkaller" <syzkaller@googlegroups.com>,
        "Sasha Levin" <sasha.levin@oracle.com>
Subject: Re: sound: uninterruptible hang in snd_seq_oss_writeq_sync
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On Tue, 01 Mar 2016 13:33:27 +0100,
Dmitry Vyukov wrote:
> 
> Hello,
> 
> The following program creates an unkillable process:
.....
> The hang stack is:
> 
> [<ffffffff85309f77>] snd_seq_oss_writeq_sync+0x327/0x790
> sound/core/seq/oss/seq_oss_writeq.c:121

This is 
	wait_event_interruptible_timeout(q->sync_sleep, ! q->sync_event_put, HZ);

and this should return zero
	if (signal_pending(current))
		/* interrupted - return 0 to finish sync */
		q->sync_event_put = 0;
	if (! q->sync_event_put || q->sync_time >= time)
		return 0;
	return 1;

> [<ffffffff852fa353>] snd_seq_oss_drain_write+0x113/0x160

... and this loop should break:
		while (snd_seq_oss_writeq_sync(dp->writeq))
			;

So, I see no obvious error in the code, so far.

I'm running your test program now with 8 parallel runs, but I couldn't
reproduce it.  Any other specifics?


thanks,

Takashi