linux-kernel - Re: sound: uninterruptible hang in snd_seq_oss_writeq

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Date:	Tue, 01 Mar 2016 15:44:58 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	"Dmitry Vyukov" <dvyukov@...gle.com>
Cc:	<alsa-devel@...a-project.org>, "Jaroslav Kysela" <perex@...ex.cz>,
	"LKML" <linux-kernel@...r.kernel.org>,
	"Alexander Potapenko" <glider@...gle.com>,
	"Kostya Serebryany" <kcc@...gle.com>,
	"syzkaller" <syzkaller@...glegroups.com>,
	"Sasha Levin" <sasha.levin@...cle.com>
Subject: Re: sound: uninterruptible hang in snd_seq_oss_writeq_sync

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