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>

diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
index 707eb2a9d50cccf15194da52479ae564a04cabed..930def8201f411d37de4652d977b5f15b75640a5 100644 (file)
--- 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);