Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | Date | Mon, 26 Nov 2018 09:36:53 +0100 | From | Takashi Iwai <> | Subject | Re: [PATCH] ALSA: pcm: Fix starvation on down_write_nonblock() |
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On Mon, 26 Nov 2018 06:36:37 +0100, Chanho Min wrote: > > Commit 67ec1072b053 ("ALSA: pcm: Fix rwsem deadlock for non-atomic PCM stream") > fixes deadlock for non-atomic PCM stream. But, This patch causes antother stuck. > If writer is RT thread and reader is a normal thread, the reader thread will > be difficult to get scheduled. It may not give chance to release readlocks > and writer gets stuck for a long time if they are pinned to single cpu. > > The deadlock described in the previous commit is because the linux rwsem > queues like a FIFO. So, we might need non-FIFO writelock, not non-block one. > > My suggestion is that the writer gives reader a chance to be scheduled by using > the minimum msleep() instaed of spinning without blocking by writer. Also, > The *_nonblock may be changed to *_nonfifo appropriately to this concept. > In terms of performance, when trylock is failed, this minimum periodic msleep > will have the same performance as the tick-based schedule()/wake_up_q(). > > Suggested-by: Wonmin Jung <wonmin.jung@lge.com> > Signed-off-by: Chanho Min <chanho.min@lge.com>
Hrm, converting unconditionally with msleep() looks too drastic.
I guess you've hit this while not explicitly using the linked PCM streams, i.e. in the call of snd_pcm_unlink() at close, right?
Then this can be worked around by checking the link before calling it. Could you check the patch below?
thanks,
Takashi
--- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -2369,7 +2369,8 @@ int snd_pcm_hw_constraints_complete(struct snd_pcm_substream *substream) static void pcm_release_private(struct snd_pcm_substream *substream) { - snd_pcm_unlink(substream); + if (snd_pcm_stream_linked(substream)) + snd_pcm_unlink(substream); } void snd_pcm_release_substream(struct snd_pcm_substream *substream)
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