[alsa-devel] sound: uninterruptible hang in snd_seq_oss_writeq_sync

[Dmitry Vyukov]

On Tue, Mar 1, 2016 at 3:44 PM, Takashi Iwai <tiwai at suse.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