Hi,
On Sep 30 2018 23:32, Thomas Gläßle wrote:
on both my desktop and laptop (archlinux), `alsactl monitor` beginns
spinning at 100% cpu when I unplug my USB headset. This happens every
time and can be reproduced as follows:
- plug in USB headphones
- start `alsactl monitor`
- unplug headphones
It happens only if the headphones are already plugged in when starting
alsactl.
The increased activity does not lead to spamming stdout or similar,
alsactl continues to perform seemingly correct, i.e. reports when I
change volume levels etc, but nothing apart from the ordinary.
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.
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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