4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Takashi Iwai tiwai@suse.de
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
--- sound/core/pcm_native.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -2370,7 +2370,8 @@ int snd_pcm_hw_constraints_complete(stru
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)