ALSA PCM OSS layer calls the generic __snd_pcm_lib_xfer() helper for
the actual transfer of the audio data. The xfer helper may sleep long
for waiting for the enough space becoming empty for read/write, and
it does unlock/relock for the substream lock. This works fine, so
far, but a slight problem specific to OSS layer is that OSS layer
wraps yet more mutex (runtime->oss.params_lock) over
__snd_pcm_lib_xfer() call; so this mutex is still locked during a
possible long sleep, and it prevents the whole ioctl and other actions
applied to the given stream.
This patch adds the temporarily unlock and relock of the mutex around
__snd_pcm_lib_xfer() call in the OSS layer to be more friendly to the
concurrent accesses. The long mutex protection itself shouldn't be a
real issue for the normal systems, and its influence appears only on
strange things like fuzzers.
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---
sound/core/oss/pcm_oss.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
index 707eb2a9d50c..930def8201f4 100644
--- a/sound/core/oss/pcm_oss.c
+++ b/sound/core/oss/pcm_oss.c
@@ -1217,8 +1217,10 @@ snd_pcm_sframes_t snd_pcm_oss_write3(struct snd_pcm_substream *substream, const
if (ret < 0)
break;
}
+ mutex_unlock(&runtime->oss.params_lock);
ret = __snd_pcm_lib_xfer(substream, (void *)ptr, true,
frames, in_kernel);
+ mutex_lock(&runtime->oss.params_lock);
if (ret != -EPIPE && ret != -ESTRPIPE)
break;
/* test, if we can't store new data, because the stream */
@@ -1254,8 +1256,10 @@ snd_pcm_sframes_t snd_pcm_oss_read3(struct snd_pcm_substream *substream, char *p
ret = snd_pcm_oss_capture_position_fixup(substream, &delay);
if (ret < 0)
break;
+ mutex_unlock(&runtime->oss.params_lock);
ret = __snd_pcm_lib_xfer(substream, (void *)ptr, true,
frames, in_kernel);
+ mutex_lock(&runtime->oss.params_lock);
if (ret == -EPIPE) {
if (runtime->status->state == SNDRV_PCM_STATE_DRAINING) {
ret = snd_pcm_kernel_ioctl(substream, SNDRV_PCM_IOCTL_DROP, NULL);
--
2.16.4
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