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[ilia <question78789@xxxxxxxxxxxxxxxxxxxxx>]

Question #78789 on alsa-lib in ubuntu changed:
https://answers.launchpad.net/ubuntu/+source/alsa-lib/+question/78789

ilia posted a new comment:
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.

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