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ALSA: pcm: Call snd_pcm_unlink() conditionally at closing

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commit b51abed8355e5556886623b2772fa6b7598d2282 upstream.

Currently the PCM core calls snd_pcm_unlink() always unconditionally
at closing a stream.  However, since snd_pcm_unlink() invokes the
global rwsem down, the lock can be easily contended.  More badly, when
a thread runs in a high priority RT-FIFO, it may stall at spinning.

Basically the call of snd_pcm_unlink() is required only for the linked
streams that are already rare occasion.  For normal use cases, this
code path is fairly superfluous.

As an optimization (and also as a workaround for the RT problem
above in normal situations without linked streams), this patch adds a
check before calling snd_pcm_unlink() and calls it only when needed.

Reported-by: Chanho Min <chanho.min@lge.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Takashi Iwai 2018-11-29 08:02:49 +01:00 committed by Greg Kroah-Hartman
parent 2ec5d37754
commit 1b5c6d035a
1 changed files with 2 additions and 1 deletions
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3
sound/core/pcm_native.c
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@ -2225,7 +2225,8 @@ 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)