Commit 146f6697 authored Feb 14, 2020 by Takashi Iwai

ALSA: pcm: oss: Unlock mutex temporarily for sleeping at read/write

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.

Link: https://lore.kernel.org/r/20200214171643.26212-1-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>

parent e9a0ef0b

sound/core/oss/pcm_oss.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -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);

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