This may be slightly off-topic but I know there are some Jack experts here.
I usually use a Zoom R24 as audio interface, sometimes with ALSA, sometimes with JACK.
Recently I got into the situation that my workstation seemed frozen. The display was frozen to the time that ‘something’ happened, keyboard, mouse (and all other usb devices) were non-functional. I could get access using a remote terminal and noticed that the jack daemon was running ot full speed. After killing the jack daemon the system became responsive again and everything turns out to be fine.
Probable cause was that I accidentally disconnected the R24 while it had connections to the running jack daemon. Okay, lesson learned.
My question to the experts: Is this expected behaviour? I.e. can jackd lock up (parts of) the Linux kernel when a device is diconnected?
I’m not an “expert” other than I enjoy using it every day given I use Ardour with Grandorgue and Aeolus via JACK. I can’t recreate your workstation freeze by disconnecting my USB device. I’ve unplugged it 5 times with no ill effects to the rest of the system. That said, I did manage to make Cadence unresponsive on the final unplug and had to kill jackdbus in order to open Cadence again but everything else was fine. I also noted that the jackdbus resources jumped from 1% to ~18% immediately after I unplugged the device. Is this what you meant by “full speed”?
Out of interest, which kernel are you using?
The situation I had was that somehow the usb bus/driver got stuck. Any program that interacted with usb froze (became unresponsive) and couldn’t even be killed. After I killed the jack daemon everything started flowing again.
I cannot exactly reproduce the issue. I tried disconnecting the R24 with jack active, the jack daemon immedeately jumps from its normal 2-3%CPU to 100%. The load of the system gradually increases in about 10 minutes to a value of 15 but then it stabilizes. And there is no lockup.
I’m running Fedora 31, with kernel 5.8.18.
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