[alsa-devel] alsactl monitor spins at 100% cpu after unplugging USB headphones

[Thomas Gläßle]

Takashi Sakamoto wrote on 10/2/18 11:01 AM:
> Thank you for this report and I can regenerate this problem.
>
> $ strace alsactl monitor
> ...
> (disconnect my sound device)
> poll([{fd=3, events=POLLIN|POLLERR|POLLNVAL}, {fd=4,
> events=POLLIN|POLLERR|POLLNVAL}, {fd=5,
> events=POLLIN|POLLERR|POLLNVAL}], 3, -1) = 1 ([{fd=5,
> revents=POLLERR|POLLNVAL}])
> poll([{fd=3, events=POLLIN|POLLERR|POLLNVAL}, {fd=4,
> events=POLLIN|POLLERR|POLLNVAL}, {fd=5,
> events=POLLIN|POLLERR|POLLNVAL}], 3, -1) = 1 ([{fd=5,
> revents=POLLERR|POLLNVAL}])
> ...
>
> This is a bug of alsactl due to handling return code of poll(2) system
> call[1].
>
> In an operation to ALSA control character devices, when handled device
> is disconnected, a call of poll(2) returns positive value to notify
> events with 'EPOLLERR | EPOLLNVAL'[2].
>
> Soon I'll post a patch to improve this behaviour of alsactl.

Thank you a lot, this is great news!

Cheers, Thomas


>
>> I'm sorry if this is not the right place to report this issue or if the
>> problem is already, I couldn't find anything about it.
>>
>>
>> Below is the output from alsa-info.sh:
>>
>> with headphones:
>>
>> http://www.alsa-project.org/db/?f=0dfc632e3adafb8bc78a182e0a225bcb13bea9fa
>>
>>
>> after unplugging:
>>
>> http://www.alsa-project.org/db/?f=41dbf0735fdd7cd2416a6b4a602505715d25b44f
>>
>>
>> Please let me know if you need further info.
>
> You did enough good. Thank you and wait for a while till I'll fix it.
>
> [1]
> http://git.alsa-project.org/?p=alsa-utils.git;a=blob;f=alsactl/monitor.c;hb=HEAD#l120
> [2]
> https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/tree/sound/core/init.c?h=for-next#n347
>
>
> Takashi Sakamoto
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