On p 1 2017 20:58, Takashi Iwai wrote:
>From 07d61ba2a1c0e06e914443225e194d99f2d8c58d Mon Sep 17 00:00:00 2001
From: Takashi Sakamoto <o-taka...@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-taka...@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
