When a USB audio device is disconnected, snd_usb_audio_disconnect() kills all audio URBs. At the same time, the application, after being notified of the disconnection, might close the device, in which case ALSA calls the .hw_free callback, which should free the URBs too.
Commit de1b8b93a0ba prevented snd_usb_hw_free() from freeing the URBs to avoid a hang that resulted from this race, but this introduced another race because the URB callbacks could now be executed after snd_usb_hw_free() has returned, and try to access already freed data.
Fix the first race by introducing a mutex to serialize the disconnect callback and all PCM callbacks that manage URBs (hw_free and hw_params).
Reported-by: Pierre-Louis Bossart pierre-louis.bossart@intel.com [CL: also serialize hw_params callback] Signed-off-by: Clemens Ladisch clemens@ladisch.de
Ah, I forgot to put my sign-off since I was waiting for any test result... Has anyone tried it?
Doesn't work for me. same oops as before. Either I made a mistake when merging this patch manually (there were some rejects), or the problem is still there. -Pierre