On 20. 03. 23 15:28, Takashi Iwai wrote:
The recent support of low latency playback in USB-audio driver made
the snd_usb_queue_pending_output_urbs() function to be called via PCM
ack ops. In the new code path, the function is performed alread in
the PCM stream lock. The problem is that, when an XRUN is detected,
the function calls snd_pcm_xrun() to notify, but snd_pcm_xrun() is
supposed to be called only outside the stream lock. As a result, it
leads to a deadlock of PCM stream locking.
For avoiding such a recursive locking, this patch adds an additional
check to the code paths in PCM core that call the ack callback; now it
checks the error code from the callback, and if it's -EPIPE, the XRUN
is handled in the PCM core side gracefully. Along with it, the
USB-audio driver code is changed to follow that, i.e. -EPIPE is
returned instead of the explicit snd_pcm_xrun() call when the function
is performed already in the stream lock.
Fixes: d5f871f89e21 ("ALSA: usb-audio: Improved lowlatency playback support")
Reported-and-tested-by: John Keeping <john@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230317195128.3911155-1-john@xxxxxxxxxxxx
Cc: Takashi Sakamoto <o-takashi@xxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
I think that this is the best variant of the proposed solutions.
Reviewed-by: Jaroslav Kysela <perex@xxxxxxxx>
Jaroslav
--
Jaroslav Kysela <perex@xxxxxxxx>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.
