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)