[PATCH v2 0/2] ASoC DPCM lockdep fixes

[PATCH v2 0/2] ASoC DPCM lockdep fixes

[Takashi Iwai]

Hi,

this is the revised patches for addressing ASoC lockdep warnings due
to the recent DPCM locking refactoring.


Takashi

v1->v2:
  - minor correction in the changelog for nested lock
  - debugfs removal workaround

===

Takashi Iwai (2):
  ASoC: soc-pcm: Fix DPCM lockdep warning due to nested stream locks
  ASoC: soc-pcm: Move debugfs removal out of spinlock

 include/sound/pcm.h     | 15 +++++++++++++++
 sound/core/pcm_native.c | 13 +++++++++++++
 sound/soc/soc-pcm.c     | 18 ++++++++++++------
 3 files changed, 40 insertions(+), 6 deletions(-)

-- 
2.31.1

[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@redhat.com>
Reported-and-tested-by: Marek Szyprowski <m.szyprowski@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@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

[PATCH v2 2/2] ASoC: soc-pcm: Move debugfs removal out of spinlock

[Takashi Iwai]

The recent fix for DPCM locking also covered the loop in
dpcm_be_disconnect() with the FE stream lock.  This caused an
unexpected side effect, thought: calling debugfs_remove_recursive() in
the spinlock may lead to lockdep splats as the code there assumes the
SOFTIRQ-safe context.

For avoiding the problem, this patch changes the disconnection
procedure to two phases: at first, the matching entries are removed
from the linked list, then the resources are freed outside the lock.

Fixes: b7898396f4bb ("ASoC: soc-pcm: Fix and cleanup DPCM locking")
Reported-and-tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/soc/soc-pcm.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
index e8876e65c649..9a954680d492 100644
--- a/sound/soc/soc-pcm.c
+++ b/sound/soc/soc-pcm.c
@@ -1268,6 +1268,7 @@ static void dpcm_be_reparent(struct snd_soc_pcm_runtime *fe,
 void dpcm_be_disconnect(struct snd_soc_pcm_runtime *fe, int stream)
 {
 	struct snd_soc_dpcm *dpcm, *d;
+	LIST_HEAD(deleted_dpcms);
 
 	snd_soc_dpcm_mutex_assert_held(fe);
 
@@ -1287,13 +1288,18 @@ void dpcm_be_disconnect(struct snd_soc_pcm_runtime *fe, int stream)
 		/* BEs still alive need new FE */
 		dpcm_be_reparent(fe, dpcm->be, stream);
 
-		dpcm_remove_debugfs_state(dpcm);
-
 		list_del(&dpcm->list_be);
+		list_move(&dpcm->list_fe, &deleted_dpcms);
+	}
+	snd_soc_dpcm_stream_unlock_irq(fe, stream);
+
+	while (!list_empty(&deleted_dpcms)) {
+		dpcm = list_first_entry(&deleted_dpcms, struct snd_soc_dpcm,
+					list_fe);
 		list_del(&dpcm->list_fe);
+		dpcm_remove_debugfs_state(dpcm);
 		kfree(dpcm);
 	}
-	snd_soc_dpcm_stream_unlock_irq(fe, stream);
 }
 
 /* get BE for DAI widget and stream */
-- 
2.31.1

Re: [PATCH v2 0/2] ASoC DPCM lockdep fixes

[Mark Brown]

On Wed, 19 Jan 2022 16:52:47 +0100, Takashi Iwai wrote:
> this is the revised patches for addressing ASoC lockdep warnings due
> to the recent DPCM locking refactoring.
> 
> 
> Takashi
> 
> v1->v2:
>   - minor correction in the changelog for nested lock
>   - debugfs removal workaround
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git for-linus

Thanks!

[1/2] ASoC: soc-pcm: Fix DPCM lockdep warning due to nested stream locks
      commit: 3c75c0ea5da749bd1efebd1387f2e5011b8c7d78
[2/2] ASoC: soc-pcm: Move debugfs removal out of spinlock
      commit: 9f620684c1ef5a002b6622ecc7b5818e81252f48

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark