ALSA: pcm: Fix mutex unbalance in OSS emulation ioctls

BugLink: http://bugs.launchpad.net/bugs/1768429

commit f6d297df upstream.

The previous fix 40cab6e8 ("ALSA: pcm: Return -EBUSY for OSS
ioctls changing busy streams") introduced some mutex unbalance; the
check of runtime->oss.rw_ref was inserted in a wrong place after the
mutex lock.

This patch fixes the inconsistency by rewriting with the helper
functions to lock/unlock parameters with the stream check.

Fixes: 40cab6e8 ("ALSA: pcm: Return -EBUSY for OSS ioctls changing busy streams")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

sound/core/oss/pcm_oss.c

@@ -833,6 +833,23 @@ static int choose_rate(struct snd_pcm_substream *substream,
 	return snd_pcm_hw_param_near(substream, params, SNDRV_PCM_HW_PARAM_RATE, best_rate, NULL);
 }
 
+/* parameter locking: returns immediately if tried during streaming */
+static int lock_params(struct snd_pcm_runtime *runtime)
+{
+	if (mutex_lock_interruptible(&runtime->oss.params_lock))
+		return -ERESTARTSYS;
+	if (atomic_read(&runtime->oss.rw_ref)) {
+		mutex_unlock(&runtime->oss.params_lock);
+		return -EBUSY;
+	}
+	return 0;
+}
+
+static void unlock_params(struct snd_pcm_runtime *runtime)
+{
+	mutex_unlock(&runtime->oss.params_lock);
+}
+
 /* call with params_lock held */
 static int snd_pcm_oss_change_params_locked(struct snd_pcm_substream *substream)
 {
@@ -1772,6 +1789,8 @@ static int snd_pcm_oss_set_rate(struct snd_pcm_oss_file *pcm_oss_file, int rate)
 	for (idx = 1; idx >= 0; --idx) {
 		struct snd_pcm_substream *substream = pcm_oss_file->streams[idx];
 		struct snd_pcm_runtime *runtime;
+		int err;
+
 		if (substream == NULL)
 			continue;
 		runtime = substream->runtime;
@@ -1779,15 +1798,14 @@ static int snd_pcm_oss_set_rate(struct snd_pcm_oss_file *pcm_oss_file, int rate)
 			rate = 1000;
 		else if (rate > 192000)
 			rate = 192000;
-		if (mutex_lock_interruptible(&runtime->oss.params_lock))
-			return -ERESTARTSYS;
-		if (atomic_read(&runtime->oss.rw_ref))
-			return -EBUSY;
+		err = lock_params(runtime);
+		if (err < 0)
+			return err;
 		if (runtime->oss.rate != rate) {
 			runtime->oss.params = 1;
 			runtime->oss.rate = rate;
 		}
-		mutex_unlock(&runtime->oss.params_lock);
+		unlock_params(runtime);
 	}
 	return snd_pcm_oss_get_rate(pcm_oss_file);
 }
@@ -1812,18 +1830,19 @@ static int snd_pcm_oss_set_channels(struct snd_pcm_oss_file *pcm_oss_file, unsig
 	for (idx = 1; idx >= 0; --idx) {
 		struct snd_pcm_substream *substream = pcm_oss_file->streams[idx];
 		struct snd_pcm_runtime *runtime;
+		int err;
+
 		if (substream == NULL)
 			continue;
 		runtime = substream->runtime;
-		if (mutex_lock_interruptible(&runtime->oss.params_lock))
-			return -ERESTARTSYS;
-		if (atomic_read(&runtime->oss.rw_ref))
-			return -EBUSY;
+		err = lock_params(runtime);
+		if (err < 0)
+			return err;
 		if (runtime->oss.channels != channels) {
 			runtime->oss.params = 1;
 			runtime->oss.channels = channels;
 		}
-		mutex_unlock(&runtime->oss.params_lock);
+		unlock_params(runtime);
 	}
 	return snd_pcm_oss_get_channels(pcm_oss_file);
 }
@@ -1896,6 +1915,7 @@ static int snd_pcm_oss_get_formats(struct snd_pcm_oss_file *pcm_oss_file)
 static int snd_pcm_oss_set_format(struct snd_pcm_oss_file *pcm_oss_file, int format)
 {
 	int formats, idx;
+	int err;
 	
 	if (format != AFMT_QUERY) {
 		formats = snd_pcm_oss_get_formats(pcm_oss_file);
@@ -1909,15 +1929,14 @@ static int snd_pcm_oss_set_format(struct snd_pcm_oss_file *pcm_oss_file, int for
 			if (substream == NULL)
 				continue;
 			runtime = substream->runtime;
-			if (atomic_read(&runtime->oss.rw_ref))
-				return -EBUSY;
-			if (mutex_lock_interruptible(&runtime->oss.params_lock))
-				return -ERESTARTSYS;
+			err = lock_params(runtime);
+			if (err < 0)
+				return err;
 			if (runtime->oss.format != format) {
 				runtime->oss.params = 1;
 				runtime->oss.format = format;
 			}
-			mutex_unlock(&runtime->oss.params_lock);
+			unlock_params(runtime);
 		}
 	}
 	return snd_pcm_oss_get_format(pcm_oss_file);
@@ -1965,12 +1984,11 @@ static int snd_pcm_oss_set_subdivide(struct snd_pcm_oss_file *pcm_oss_file, int
 		if (substream == NULL)
 			continue;
 		runtime = substream->runtime;
-		if (atomic_read(&runtime->oss.rw_ref))
-			return -EBUSY;
-		if (mutex_lock_interruptible(&runtime->oss.params_lock))
-			return -ERESTARTSYS;
+		err = lock_params(runtime);
+		if (err < 0)
+			return err;
 		err = snd_pcm_oss_set_subdivide1(substream, subdivide);
-		mutex_unlock(&runtime->oss.params_lock);
+		unlock_params(runtime);
 		if (err < 0)
 			return err;
 	}
@@ -2005,12 +2023,11 @@ static int snd_pcm_oss_set_fragment(struct snd_pcm_oss_file *pcm_oss_file, unsig
 		if (substream == NULL)
 			continue;
 		runtime = substream->runtime;
-		if (atomic_read(&runtime->oss.rw_ref))
-			return -EBUSY;
-		if (mutex_lock_interruptible(&runtime->oss.params_lock))
-			return -ERESTARTSYS;
+		err = lock_params(runtime);
+		if (err < 0)
+			return err;
 		err = snd_pcm_oss_set_fragment1(substream, val);
-		mutex_unlock(&runtime->oss.params_lock);
+		unlock_params(runtime);
 		if (err < 0)
 			return err;
 	}