Merge branch 'topic/pcm-lock-refactor' into for-next

Pull PCM lock refactoring.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/pcm.h

@@ -30,6 +30,7 @@
 #include <linux/mm.h>
 #include <linux/bitops.h>
 #include <linux/pm_qos.h>
+#include <linux/refcount.h>
 
 #define snd_pcm_substream_chip(substream) ((substream)->private_data)
 #define snd_pcm_chip(pcm) ((pcm)->private_data)
@@ -439,7 +440,7 @@ struct snd_pcm_group {		/* keep linked substreams */
 	spinlock_t lock;
 	struct mutex mutex;
 	struct list_head substreams;
-	int count;
+	refcount_t refs;
 };
 
 struct pid;

sound/core/pcm.c

@@ -733,9 +733,7 @@ int snd_pcm_new_stream(struct snd_pcm *pcm, int stream, int substream_count)
 			}
 		}
 		substream->group = &substream->self_group;
-		spin_lock_init(&substream->self_group.lock);
-		mutex_init(&substream->self_group.mutex);
-		INIT_LIST_HEAD(&substream->self_group.substreams);
+		snd_pcm_group_init(&substream->self_group);
 		list_add_tail(&substream->link_list, &substream->self_group.substreams);
 		atomic_set(&substream->mmap_count, 0);
 		prev = substream;

sound/core/pcm_local.h

@@ -66,5 +66,6 @@ static inline void snd_pcm_timer_done(struct snd_pcm_substream *substream) {}
 #endif
 
 void __snd_pcm_xrun(struct snd_pcm_substream *substream);
+void snd_pcm_group_init(struct snd_pcm_group *group);
 
 #endif	/* __SOUND_CORE_PCM_LOCAL_H */

sound/core/pcm_native.c

@@ -85,71 +85,30 @@ static int snd_pcm_open(struct file *file, struct snd_pcm *pcm, int stream);
  *
  */
 
-static DEFINE_RWLOCK(snd_pcm_link_rwlock);
 static DECLARE_RWSEM(snd_pcm_link_rwsem);
 
-/* Writer in rwsem may block readers even during its waiting in queue,
- * and this may lead to a deadlock when the code path takes read sem
- * twice (e.g. one in snd_pcm_action_nonatomic() and another in
- * snd_pcm_stream_lock()).  As a (suboptimal) workaround, let writer to
- * sleep until all the readers are completed without blocking by writer.
- */
-static inline void down_write_nonfifo(struct rw_semaphore *lock)
+void snd_pcm_group_init(struct snd_pcm_group *group)
 {
-	while (!down_write_trylock(lock))
-		msleep(1);
+	spin_lock_init(&group->lock);
+	mutex_init(&group->mutex);
+	INIT_LIST_HEAD(&group->substreams);
+	refcount_set(&group->refs, 0);
 }
 
-#define PCM_LOCK_DEFAULT	0
-#define PCM_LOCK_IRQ	1
-#define PCM_LOCK_IRQSAVE	2
-
-static unsigned long __snd_pcm_stream_lock_mode(struct snd_pcm_substream *substream,
-						unsigned int mode)
-{
-	unsigned long flags = 0;
-	if (substream->pcm->nonatomic) {
-		down_read_nested(&snd_pcm_link_rwsem, SINGLE_DEPTH_NESTING);
-		mutex_lock(&substream->self_group.mutex);
-	} else {
-		switch (mode) {
-		case PCM_LOCK_DEFAULT:
-			read_lock(&snd_pcm_link_rwlock);
-			break;
-		case PCM_LOCK_IRQ:
-			read_lock_irq(&snd_pcm_link_rwlock);
-			break;
-		case PCM_LOCK_IRQSAVE:
-			read_lock_irqsave(&snd_pcm_link_rwlock, flags);
-			break;
-		}
-		spin_lock(&substream->self_group.lock);
-	}
-	return flags;
+/* define group lock helpers */
+#define DEFINE_PCM_GROUP_LOCK(action, mutex_action) \
+static void snd_pcm_group_ ## action(struct snd_pcm_group *group, bool nonatomic) \
+{ \
+	if (nonatomic) \
+		mutex_ ## mutex_action(&group->mutex); \
+	else \
+		spin_ ## action(&group->lock); \
 }
 
-static void __snd_pcm_stream_unlock_mode(struct snd_pcm_substream *substream,
-					 unsigned int mode, unsigned long flags)
-{
-	if (substream->pcm->nonatomic) {
-		mutex_unlock(&substream->self_group.mutex);
-		up_read(&snd_pcm_link_rwsem);
-	} else {
-		spin_unlock(&substream->self_group.lock);
-
-		switch (mode) {
-		case PCM_LOCK_DEFAULT:
-			read_unlock(&snd_pcm_link_rwlock);
-			break;
-		case PCM_LOCK_IRQ:
-			read_unlock_irq(&snd_pcm_link_rwlock);
-			break;
-		case PCM_LOCK_IRQSAVE:
-			read_unlock_irqrestore(&snd_pcm_link_rwlock, flags);
-			break;
-		}
-	}
-}
+DEFINE_PCM_GROUP_LOCK(lock, lock);
+DEFINE_PCM_GROUP_LOCK(unlock, unlock);
+DEFINE_PCM_GROUP_LOCK(lock_irq, lock);
+DEFINE_PCM_GROUP_LOCK(unlock_irq, unlock);
 
 /**
  * snd_pcm_stream_lock - Lock the PCM stream
@@ -161,7 +120,7 @@ static void __snd_pcm_stream_unlock_mode(struct snd_pcm_substream *substream,
  */
 void snd_pcm_stream_lock(struct snd_pcm_substream *substream)
 {
-	__snd_pcm_stream_lock_mode(substream, PCM_LOCK_DEFAULT);
+	snd_pcm_group_lock(&substream->self_group, substream->pcm->nonatomic);
 }
 EXPORT_SYMBOL_GPL(snd_pcm_stream_lock);
 
@@ -173,7 +132,7 @@ EXPORT_SYMBOL_GPL(snd_pcm_stream_lock);
  */
 void snd_pcm_stream_unlock(struct snd_pcm_substream *substream)
 {
-	__snd_pcm_stream_unlock_mode(substream, PCM_LOCK_DEFAULT, 0);
+	snd_pcm_group_unlock(&substream->self_group, substream->pcm->nonatomic);
 }
 EXPORT_SYMBOL_GPL(snd_pcm_stream_unlock);
 
@@ -187,7 +146,8 @@ EXPORT_SYMBOL_GPL(snd_pcm_stream_unlock);
  */
 void snd_pcm_stream_lock_irq(struct snd_pcm_substream *substream)
 {
-	__snd_pcm_stream_lock_mode(substream, PCM_LOCK_IRQ);
+	snd_pcm_group_lock_irq(&substream->self_group,
+			       substream->pcm->nonatomic);
 }
 EXPORT_SYMBOL_GPL(snd_pcm_stream_lock_irq);
 
@@ -199,13 +159,19 @@ EXPORT_SYMBOL_GPL(snd_pcm_stream_lock_irq);
  */
 void snd_pcm_stream_unlock_irq(struct snd_pcm_substream *substream)
 {
-	__snd_pcm_stream_unlock_mode(substream, PCM_LOCK_IRQ, 0);
+	snd_pcm_group_unlock_irq(&substream->self_group,
+				 substream->pcm->nonatomic);
 }
 EXPORT_SYMBOL_GPL(snd_pcm_stream_unlock_irq);
 
 unsigned long _snd_pcm_stream_lock_irqsave(struct snd_pcm_substream *substream)
 {
-	return __snd_pcm_stream_lock_mode(substream, PCM_LOCK_IRQSAVE);
+	unsigned long flags = 0;
+	if (substream->pcm->nonatomic)
+		mutex_lock(&substream->self_group.mutex);
+	else
+		spin_lock_irqsave(&substream->self_group.lock, flags);
+	return flags;
 }
 EXPORT_SYMBOL_GPL(_snd_pcm_stream_lock_irqsave);
 
@@ -219,7 +185,10 @@ EXPORT_SYMBOL_GPL(_snd_pcm_stream_lock_irqsave);
 void snd_pcm_stream_unlock_irqrestore(struct snd_pcm_substream *substream,
 				      unsigned long flags)
 {
-	__snd_pcm_stream_unlock_mode(substream, PCM_LOCK_IRQSAVE, flags);
+	if (substream->pcm->nonatomic)
+		mutex_unlock(&substream->self_group.mutex);
+	else
+		spin_unlock_irqrestore(&substream->self_group.lock, flags);
 }
 EXPORT_SYMBOL_GPL(snd_pcm_stream_unlock_irqrestore);
 
@@ -1124,6 +1093,68 @@ static int snd_pcm_action_single(const struct action_ops *ops,
 	return res;
 }
 
+static void snd_pcm_group_assign(struct snd_pcm_substream *substream,
+				 struct snd_pcm_group *new_group)
+{
+	substream->group = new_group;
+	list_move(&substream->link_list, &new_group->substreams);
+}
+
+/*
+ * Unref and unlock the group, but keep the stream lock;
+ * when the group becomes empty and no longer referred, destroy itself
+ */
+static void snd_pcm_group_unref(struct snd_pcm_group *group,
+				struct snd_pcm_substream *substream)
+{
+	bool do_free;
+
+	if (!group)
+		return;
+	do_free = refcount_dec_and_test(&group->refs) &&
+		list_empty(&group->substreams);
+	snd_pcm_group_unlock(group, substream->pcm->nonatomic);
+	if (do_free)
+		kfree(group);
+}
+
+/*
+ * Lock the group inside a stream lock and reference it;
+ * return the locked group object, or NULL if not linked
+ */
+static struct snd_pcm_group *
+snd_pcm_stream_group_ref(struct snd_pcm_substream *substream)
+{
+	bool nonatomic = substream->pcm->nonatomic;
+	struct snd_pcm_group *group;
+	bool trylock;
+
+	for (;;) {
+		if (!snd_pcm_stream_linked(substream))
+			return NULL;
+		group = substream->group;
+		/* block freeing the group object */
+		refcount_inc(&group->refs);
+
+		trylock = nonatomic ? mutex_trylock(&group->mutex) :
+			spin_trylock(&group->lock);
+		if (trylock)
+			break; /* OK */
+
+		/* re-lock for avoiding ABBA deadlock */
+		snd_pcm_stream_unlock(substream);
+		snd_pcm_group_lock(group, nonatomic);
+		snd_pcm_stream_lock(substream);
+
+		/* check the group again; the above opens a small race window */
+		if (substream->group == group)
+			break; /* OK */
+		/* group changed, try again */
+		snd_pcm_group_unref(group, substream);
+	}
+	return group;
+}
+
 /*
  *  Note: call with stream lock
  */
@@ -1131,28 +1162,15 @@ static int snd_pcm_action(const struct action_ops *ops,
 			  struct snd_pcm_substream *substream,
 			  int state)
 {
+	struct snd_pcm_group *group;
 	int res;
 
-	if (!snd_pcm_stream_linked(substream))
-		return snd_pcm_action_single(ops, substream, state);
-
-	if (substream->pcm->nonatomic) {
-		if (!mutex_trylock(&substream->group->mutex)) {
-			mutex_unlock(&substream->self_group.mutex);
-			mutex_lock(&substream->group->mutex);
-			mutex_lock(&substream->self_group.mutex);
-		}
-		res = snd_pcm_action_group(ops, substream, state, 1);
-		mutex_unlock(&substream->group->mutex);
-	} else {
-		if (!spin_trylock(&substream->group->lock)) {
-			spin_unlock(&substream->self_group.lock);
-			spin_lock(&substream->group->lock);
-			spin_lock(&substream->self_group.lock);
-		}
+	group = snd_pcm_stream_group_ref(substream);
+	if (group)
 		res = snd_pcm_action_group(ops, substream, state, 1);
-		spin_unlock(&substream->group->lock);
-	}
+	else
+		res = snd_pcm_action_single(ops, substream, state);
+	snd_pcm_group_unref(group, substream);
 	return res;
 }
 
@@ -1179,6 +1197,7 @@ static int snd_pcm_action_nonatomic(const struct action_ops *ops,
 {
 	int res;
 
+	/* Guarantee the group members won't change during non-atomic action */
 	down_read(&snd_pcm_link_rwsem);
 	if (snd_pcm_stream_linked(substream))
 		res = snd_pcm_action_group(ops, substream, state, 0);
@@ -1802,6 +1821,7 @@ static int snd_pcm_drain(struct snd_pcm_substream *substream,
 	struct snd_card *card;
 	struct snd_pcm_runtime *runtime;
 	struct snd_pcm_substream *s;
+	struct snd_pcm_group *group;
 	wait_queue_entry_t wait;
 	int result = 0;
 	int nonblock = 0;
@@ -1818,7 +1838,6 @@ static int snd_pcm_drain(struct snd_pcm_substream *substream,
 	} else if (substream->f_flags & O_NONBLOCK)
 		nonblock = 1;
 
-	down_read(&snd_pcm_link_rwsem);
 	snd_pcm_stream_lock_irq(substream);
 	/* resume pause */
 	if (runtime->status->state == SNDRV_PCM_STATE_PAUSED)
@@ -1843,6 +1862,7 @@ static int snd_pcm_drain(struct snd_pcm_substream *substream,
 		}
 		/* find a substream to drain */
 		to_check = NULL;
+		group = snd_pcm_stream_group_ref(substream);
 		snd_pcm_group_for_each_entry(s, substream) {
 			if (s->stream != SNDRV_PCM_STREAM_PLAYBACK)
 				continue;
@@ -1852,12 +1872,12 @@ static int snd_pcm_drain(struct snd_pcm_substream *substream,
 				break;
 			}
 		}
+		snd_pcm_group_unref(group, substream);
 		if (!to_check)
 			break; /* all drained */
 		init_waitqueue_entry(&wait, current);
 		add_wait_queue(&to_check->sleep, &wait);
 		snd_pcm_stream_unlock_irq(substream);
-		up_read(&snd_pcm_link_rwsem);
 		if (runtime->no_period_wakeup)
 			tout = MAX_SCHEDULE_TIMEOUT;
 		else {
@@ -1869,9 +1889,17 @@ static int snd_pcm_drain(struct snd_pcm_substream *substream,
 			tout = msecs_to_jiffies(tout * 1000);
 		}
 		tout = schedule_timeout_interruptible(tout);
-		down_read(&snd_pcm_link_rwsem);
+
 		snd_pcm_stream_lock_irq(substream);
-		remove_wait_queue(&to_check->sleep, &wait);
+		group = snd_pcm_stream_group_ref(substream);
+		snd_pcm_group_for_each_entry(s, substream) {
+			if (s->runtime == to_check) {
+				remove_wait_queue(&to_check->sleep, &wait);
+				break;
+			}
+		}
+		snd_pcm_group_unref(group, substream);
+
 		if (card->shutdown) {
 			result = -ENODEV;
 			break;
@@ -1891,7 +1919,6 @@ static int snd_pcm_drain(struct snd_pcm_substream *substream,
 
  unlock:
 	snd_pcm_stream_unlock_irq(substream);
-	up_read(&snd_pcm_link_rwsem);
 
 	return result;
 }
@@ -1930,13 +1957,19 @@ static int snd_pcm_drop(struct snd_pcm_substream *substream)
 static bool is_pcm_file(struct file *file)
 {
 	struct inode *inode = file_inode(file);
+	struct snd_pcm *pcm;
 	unsigned int minor;
 
 	if (!S_ISCHR(inode->i_mode) || imajor(inode) != snd_major)
 		return false;
 	minor = iminor(inode);
-	return snd_lookup_minor_data(minor, SNDRV_DEVICE_TYPE_PCM_PLAYBACK) ||
-		snd_lookup_minor_data(minor, SNDRV_DEVICE_TYPE_PCM_CAPTURE);
+	pcm = snd_lookup_minor_data(minor, SNDRV_DEVICE_TYPE_PCM_PLAYBACK);
+	if (!pcm)
+		pcm = snd_lookup_minor_data(minor, SNDRV_DEVICE_TYPE_PCM_CAPTURE);
+	if (!pcm)
+		return false;
+	snd_card_unref(pcm->card);
+	return true;
 }
 
 /*
@@ -1947,7 +1980,8 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
 	int res = 0;
 	struct snd_pcm_file *pcm_file;
 	struct snd_pcm_substream *substream1;
-	struct snd_pcm_group *group;
+	struct snd_pcm_group *group, *target_group;
+	bool nonatomic = substream->pcm->nonatomic;
 	struct fd f = fdget(fd);
 
 	if (!f.file)
@@ -1958,13 +1992,14 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
 	}
 	pcm_file = f.file->private_data;
 	substream1 = pcm_file->substream;
-	group = kmalloc(sizeof(*group), GFP_KERNEL);
+	group = kzalloc(sizeof(*group), GFP_KERNEL);
 	if (!group) {
 		res = -ENOMEM;
 		goto _nolock;
 	}
-	down_write_nonfifo(&snd_pcm_link_rwsem);
-	write_lock_irq(&snd_pcm_link_rwlock);
+	snd_pcm_group_init(group);
+
+	down_write(&snd_pcm_link_rwsem);
 	if (substream->runtime->status->state == SNDRV_PCM_STATE_OPEN ||
 	    substream->runtime->status->state != substream1->runtime->status->state ||
 	    substream->pcm->nonatomic != substream1->pcm->nonatomic) {
@@ -1975,23 +2010,23 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
 		res = -EALREADY;
 		goto _end;
 	}
+
+	snd_pcm_stream_lock_irq(substream);
 	if (!snd_pcm_stream_linked(substream)) {
-		substream->group = group;
-		group = NULL;
-		spin_lock_init(&substream->group->lock);
-		mutex_init(&substream->group->mutex);
-		INIT_LIST_HEAD(&substream->group->substreams);
-		list_add_tail(&substream->link_list, &substream->group->substreams);
-		substream->group->count = 1;
-	}
-	list_add_tail(&substream1->link_list, &substream->group->substreams);
-	substream->group->count++;
-	substream1->group = substream->group;
+		snd_pcm_group_assign(substream, group);
+		group = NULL; /* assigned, don't free this one below */
+	}
+	target_group = substream->group;
+	snd_pcm_stream_unlock_irq(substream);
+
+	snd_pcm_group_lock_irq(target_group, nonatomic);
+	snd_pcm_stream_lock(substream1);
+	snd_pcm_group_assign(substream1, target_group);
+	snd_pcm_stream_unlock(substream1);
+	snd_pcm_group_unlock_irq(target_group, nonatomic);
  _end:
-	write_unlock_irq(&snd_pcm_link_rwlock);
 	up_write(&snd_pcm_link_rwsem);
  _nolock:
-	snd_card_unref(substream1->pcm->card);
 	kfree(group);
  _badf:
 	fdput(f);
@@ -2000,34 +2035,43 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
 
 static void relink_to_local(struct snd_pcm_substream *substream)
 {
-	substream->group = &substream->self_group;
-	INIT_LIST_HEAD(&substream->self_group.substreams);
-	list_add_tail(&substream->link_list, &substream->self_group.substreams);
+	snd_pcm_stream_lock(substream);
+	snd_pcm_group_assign(substream, &substream->self_group);
+	snd_pcm_stream_unlock(substream);
 }
 
 static int snd_pcm_unlink(struct snd_pcm_substream *substream)
 {
-	struct snd_pcm_substream *s;
+	struct snd_pcm_group *group;
+	bool nonatomic = substream->pcm->nonatomic;
+	bool do_free = false;
 	int res = 0;
 
-	down_write_nonfifo(&snd_pcm_link_rwsem);
-	write_lock_irq(&snd_pcm_link_rwlock);
+	down_write(&snd_pcm_link_rwsem);
+
 	if (!snd_pcm_stream_linked(substream)) {
 		res = -EALREADY;
 		goto _end;
 	}
-	list_del(&substream->link_list);
-	substream->group->count--;
-	if (substream->group->count == 1) {	/* detach the last stream, too */
-		snd_pcm_group_for_each_entry(s, substream) {
-			relink_to_local(s);
-			break;
-		}
-		kfree(substream->group);
-	}
+
+	group = substream->group;
+	snd_pcm_group_lock_irq(group, nonatomic);
+
 	relink_to_local(substream);
+
+	/* detach the last stream, too */
+	if (list_is_singular(&group->substreams)) {
+		relink_to_local(list_first_entry(&group->substreams,
+						 struct snd_pcm_substream,
+						 link_list));
+		do_free = !refcount_read(&group->refs);
+	}
+
+	snd_pcm_group_unlock_irq(group, nonatomic);
+	if (do_free)
+		kfree(group);
+
        _end:
-	write_unlock_irq(&snd_pcm_link_rwlock);
 	up_write(&snd_pcm_link_rwsem);
 	return res;
 }