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

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Date:	Tue, 1 Mar 2016 16:01:13 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	Takashi Iwai <tiwai@...e.de>
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, Mar 1, 2016 at 3:44 PM, Takashi Iwai <tiwai@...e.de> wrote:
> 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