Messages in this thread | | | Subject | Re: [PATCH 23/25] ALSA/dummy: Replace tasklet with softirq hrtimer | From | Takashi Sakamoto <> | Date | Sat, 2 Sep 2017 10:19:45 +0900 |
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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
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