alsa suddenly stopped working (dmix socket disappeared)

I managed to fix the error with some deep black magic:

   strace -o /tmp/out mplayer -ao alsa file.mp3

watch it bomb out with an error

   grep shmget /tmp/out

get one important line:
shmget(5678293, 384, IPC_CREAT|0660) = 48824355

   shmrm -M 5678293

Looks like the process that previously acted as the dmix server died, but did not free the SysV shared memory segment.

I may have caused the problem by killing a firefox instance that stayed behind (with its 400 megs of virtual memory allocated) after I closed all of its windows.

Thanks for the report and your fix. However, we need some more info.

Has this bug reproduced itself? If so, was it in identical circumstances?

What package version of 'alsa' are you using?

What release of ubuntu are you using?

So far I've been unable to reproduce the problem.

I have Ubuntu Edgy with alsa 1.0.11-5ubuntu1.

If you can't reproduce it on your edgy installation, is it also not a problem in an edgy livecd environment?

As this can't be reproduced; i am going to reject this bug report.

Thanks again for your report - if it re-occurs please reopen this bug.

I am also suffering from this problem ( Kubuntu Edgy ).
At first glance, it does indeed seem related to an application exiting incorrectly (ie. crashing).

Using a different also application, I get:

> grep shmget /tmp/out

shmget(5678293, 384, IPC_CREAT|0660) = 134873127
shmget(IPC_PRIVATE, 21760, IPC_CREAT|0777) = 1487996561

I don't have access to shmrm, thou, to test if that also fixes it in my case. What package is that command part of?

Sorry, when I wrote 'shmrm', I was actually thinking about 'ipcrm'. It's in the util-linux package, which is installed by default.

Marius Gedminas wrote:
> Sorry, when I wrote 'shmrm', I was actually thinking about 'ipcrm'.
> It's in the util-linux package, which is installed by default.
>

Cool. I can confirm that the workaround works also for me. I had to do:
> ipcrm -M 5678293 -S 5678293

This issue seems to be due to a design problem in ALSA and dmix in Linux 2.6.17. The design was changed in 2.6.18, so the problem should go away with Feisty.

I use Feisty with 2.6.20 kernel on AMD64 platform. I have discovered a similar problem and already reported it as Bug #115593 (now, when I've found this bug description, #115593 may be marked as a duplicate, but I don't know how to do it...).
Today, when all sound applications hanged again I did one more debug session. I think, some application which used dmix was killed. I don't know dmix architecture, but I know that dmix uses semaphores and shared memory for IPC. If application which raised the semaphore exits without zeroing it (e.g. segfaults or is killed in another way), other applications will wait forever for the semaphore to lower (in my testing, semctl(sem_id, 0, GETZCNT) has returned 2). The presence of the semaphore may be checked from the command line:
  ipcs -s $IPC_KEY
where $IPC_KEY contains the value of dmix' ipc_key option. The semaphore may be deleted with:
  ipcrm -S $IPC_KEY
This return all sound applications to the working state.

IMO, the issue should be reported upstream and some watchdog should be implemented to overcome the deadlock when "important" process dies. Although I don't know the ALSA architecture, I think, changing just dmix may fix the bug (no need to touch other ALSA parts).
Since the bug is present in the latest release, it should be reopened.

Bug still exists in Feisty (see comment 10).

alsa-lib (1.0.15-2ubuntu1) hardy; urgency=low

  * Merge from Debian unstable.
  * Ubuntu-specific changes:
    - debian/libasound2.p{ostinst,rerm}: Install,remove update-notifier
      file, respectively;
    - debian/control: Add lpia to supported arches, adhere to
      DebianMaintainerField.
  * Dmix/dsnoop no longer use sockets (LP: #85157).
  * Biarch plugins support fixed (LP: #145645).

 -- Daniel T Chen <email address hidden> Sat, 01 Dec 2007 18:50:12 -0500