From bcab3a6e64a9647e022b46182c9687a8c3aa9d11 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@suse.de>
Date: Wed, 30 Aug 2017 14:50:07 +0200
Subject: [PATCH] ALSA: pcm: Fix power lock unbalance via OSS emulation
Git-commit: bcab3a6e64a9647e022b46182c9687a8c3aa9d11
Patch-mainline: v4.13
References: bsc#1121278

PCM OSS emulation issues the drain ioctl without power lock.  It used
to work in the earlier kernels as the power lock was taken inside
snd_pcm_drain() itself.  But since 68b4acd32249 ("ALSA: pcm: Apply
power lock globally to common ioctls"), the power lock is taken
outside the function.  Due to that change, the call via OSS emulation
leads to the unbalanced power lock, thus it deadlocks.

As a quick fix, just take the power lock before snd_pcm_drain() call
for OSS emulation path.  A better cleanup will follow later.

Fixes: 68b4acd32249 ("ALSA: pcm: Apply power lock globally to common ioctls")
Reported-and-tested-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

---
 sound/core/pcm_native.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 22995cb3bd44..cf0433f80067 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -3064,6 +3064,7 @@ int snd_pcm_kernel_ioctl(struct snd_pcm_substream *substream,
 {
 	snd_pcm_uframes_t *frames = arg;
 	snd_pcm_sframes_t result;
+	int err;
 	
 	switch (cmd) {
 	case SNDRV_PCM_IOCTL_FORWARD:
@@ -3083,7 +3084,10 @@ int snd_pcm_kernel_ioctl(struct snd_pcm_substream *substream,
 	case SNDRV_PCM_IOCTL_START:
 		return snd_pcm_start_lock_irq(substream);
 	case SNDRV_PCM_IOCTL_DRAIN:
-		return snd_pcm_drain(substream, NULL);
+		snd_power_lock(substream->pcm->card);
+		err = snd_pcm_drain(substream, NULL);
+		snd_power_unlock(substream->pcm->card);
+		return err;
 	case SNDRV_PCM_IOCTL_DROP:
 		return snd_pcm_drop(substream);
 	case SNDRV_PCM_IOCTL_DELAY:
-- 
2.20.1