On p 1 2017 20:58, Takashi Iwai wrote:
From 07d61ba2a1c0e06e914443225e194d99f2d8c58d Mon Sep 17 00:00:00 2001
From: Takashi Sakamoto o-takashi@sakamocchi.jp Date: Fri, 1 Sep 2017 19:10:18 +0900 Subject: [PATCH] ALSA: dummy: avoid stall due to a call of hrtimer_cancel() on a callback of hrtimer
A call of 'htrimer_cancel()' on a callback of hrtimer brings endless loop because 'struct hrtimer_clock_base.running' is not NULL on the callback. In hrtimer subsystem, this member is used to indicate the instance of hrtimer gets callbacks and there's a helper function, 'hrtimer_callback_running()' to check it.
ALSA dummy driver uses hrtimer to emulate hardware interrupt per period of PCM buffer. When XRUN occurs on PCM substream, in a call of 'snd_pcm_period_elapsed()', 'struct snd_pcm_ops.stop()' is called to stop the substream. In current implementation, 'hrtimer_cancel()' is used to wait for cancellation of hrtimer. However, as described, this brings endless loop.
It's not only about XRUN. When the stream finishes the draining, it stops the stream gracefully -- that is the very normal operation.
I overlooked it. Thanks for your indication.
For this problem, this commit uses 'hrtimer_callback_running()' to detect whether to be on a callback of hrtimer or not, then skip cancellation of hrtimer in hrtimer callbacks. Furthermore, at a case of XRUN, hrtimer callback returns HRTIMER_NORESTART after a call of 'snd_pcm_period_elapsed()' to discontinue hrtimr because cancellation is skipped.
Signed-off-by: Takashi Sakamoto o-takashi@sakamocchi.jp
It's better to fold the fix into the original patch instead of introducing a bug and fixing it.
Yep. I request the authors to include this fix.
Well, in sound subsystem, there're a few drivers which uses hrtimer: - snd-pcsp - snd-sh-dac-audio - snd-soc-imx-pcm-fiq
As a quick glance, 'snd-sh-dac-audio' includes the same bug, too. Additionally, 'snd-soc-imx-pcm-fiq' maintains hrtimer with loose manner in a point of state of PCM substream and it shall gain the same bug if improved. Later, I posted some patches for them.
Thanks
Takashi Sakamoto