[PATCH v2 1/2] ASoC: soc-pcm: Fix DPCM lockdep warning due to nested stream locks

[Takashi Iwai]

The recent change for DPCM locking caused spurious lockdep warnings.
Actually the warnings are false-positive, as those are triggered due
to the nested stream locks for FE and BE.  Since both locks belong to
the same lock class, lockdep sees it as if a deadlock.

For fixing this, we need to take PCM stream locks for BE with the
nested lock primitives.  Since currently snd_pcm_stream_lock*() helper
assumes only the top-level single locking, a new helper function
snd_pcm_stream_lock_irqsave_nested() is defined for a single-depth
nested lock, which is now used in the BE DAI trigger that is always
performed inside a FE stream lock.

Fixes: b2ae80663008 ("ASoC: soc-pcm: serialize BE triggers")
Reported-and-tested-by: Hans de Goede <hdegoede at redhat.com>
Reported-and-tested-by: Marek Szyprowski <m.szyprowski at samsung.com>
Link: https://lore.kernel.org/r/73018f3c-9769-72ea-0325-b3f8e2381e30@redhat.com
Link: https://lore.kernel.org/alsa-devel/9a0abddd-49e9-872d-2f00-a1697340f786@samsung.com
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---

v1->v2: Correct Fixes tag, a typo fix

 include/sound/pcm.h     | 15 +++++++++++++++
 sound/core/pcm_native.c | 13 +++++++++++++
 sound/soc/soc-pcm.c     |  6 +++---
 3 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index 9b187d86e1bd..36da42cd0774 100644
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -617,6 +617,7 @@ void snd_pcm_stream_unlock(struct snd_pcm_substream *substream);
 void snd_pcm_stream_lock_irq(struct snd_pcm_substream *substream);
 void snd_pcm_stream_unlock_irq(struct snd_pcm_substream *substream);
 unsigned long _snd_pcm_stream_lock_irqsave(struct snd_pcm_substream *substream);
+unsigned long _snd_pcm_stream_lock_irqsave_nested(struct snd_pcm_substream *substream);
 
 /**
  * snd_pcm_stream_lock_irqsave - Lock the PCM stream
@@ -635,6 +636,20 @@ unsigned long _snd_pcm_stream_lock_irqsave(struct snd_pcm_substream *substream);
 void snd_pcm_stream_unlock_irqrestore(struct snd_pcm_substream *substream,
 				      unsigned long flags);
 
+/**
+ * snd_pcm_stream_lock_irqsave_nested - Single-nested PCM stream locking
+ * @substream: PCM substream
+ * @flags: irq flags
+ *
+ * This locks the PCM stream like snd_pcm_stream_lock_irqsave() but with
+ * the single-depth lockdep subclass.
+ */
+#define snd_pcm_stream_lock_irqsave_nested(substream, flags)		\
+	do {								\
+		typecheck(unsigned long, flags);			\
+		flags = _snd_pcm_stream_lock_irqsave_nested(substream); \
+	} while (0)
+
 /**
  * snd_pcm_group_for_each_entry - iterate over the linked substreams
  * @s: the iterator
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 621883e71194..a056b3ef3c84 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -172,6 +172,19 @@ unsigned long _snd_pcm_stream_lock_irqsave(struct snd_pcm_substream *substream)
 }
 EXPORT_SYMBOL_GPL(_snd_pcm_stream_lock_irqsave);
 
+unsigned long _snd_pcm_stream_lock_irqsave_nested(struct snd_pcm_substream *substream)
+{
+	unsigned long flags = 0;
+	if (substream->pcm->nonatomic)
+		mutex_lock_nested(&substream->self_group.mutex,
+				  SINGLE_DEPTH_NESTING);
+	else
+		spin_lock_irqsave_nested(&substream->self_group.lock, flags,
+					 SINGLE_DEPTH_NESTING);
+	return flags;
+}
+EXPORT_SYMBOL_GPL(_snd_pcm_stream_lock_irqsave_nested);
+
 /**
  * snd_pcm_stream_unlock_irqrestore - Unlock the PCM stream
  * @substream: PCM substream
diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
index 7abfc48b26ca..e8876e65c649 100644
--- a/sound/soc/soc-pcm.c
+++ b/sound/soc/soc-pcm.c
@@ -46,8 +46,8 @@ static inline void snd_soc_dpcm_stream_lock_irq(struct snd_soc_pcm_runtime *rtd,
 	snd_pcm_stream_lock_irq(snd_soc_dpcm_get_substream(rtd, stream));
 }
 
-#define snd_soc_dpcm_stream_lock_irqsave(rtd, stream, flags) \
-	snd_pcm_stream_lock_irqsave(snd_soc_dpcm_get_substream(rtd, stream), flags)
+#define snd_soc_dpcm_stream_lock_irqsave_nested(rtd, stream, flags) \
+	snd_pcm_stream_lock_irqsave_nested(snd_soc_dpcm_get_substream(rtd, stream), flags)
 
 static inline void snd_soc_dpcm_stream_unlock_irq(struct snd_soc_pcm_runtime *rtd,
 						  int stream)
@@ -2094,7 +2094,7 @@ int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
 		be = dpcm->be;
 		be_substream = snd_soc_dpcm_get_substream(be, stream);
 
-		snd_soc_dpcm_stream_lock_irqsave(be, stream, flags);
+		snd_soc_dpcm_stream_lock_irqsave_nested(be, stream, flags);
 
 		/* is this op for this BE ? */
 		if (!snd_soc_dpcm_be_can_update(fe, be, stream))
-- 
2.31.1