Commit e18035cf authored Jun 08, 2020 by Michał Mirosław Committed by Takashi Iwai Jun 08, 2020

ALSA: pcm: fix snd_pcm_link() lockdep splat



Add and use snd_pcm_stream_lock_nested() in snd_pcm_link/unlink
implementation.  The code is fine, but generates a lockdep complaint:

============================================
WARNING: possible recursive locking detected
5.7.1mq+ #381 Tainted: G           O
--------------------------------------------
pulseaudio/4180 is trying to acquire lock:
ffff888402d6f508 (&group->lock){-...}-{2:2}, at: snd_pcm_common_ioctl+0xda8/0xee0 [snd_pcm]

but task is already holding lock:
ffff8883f7a8cf18 (&group->lock){-...}-{2:2}, at: snd_pcm_common_ioctl+0xe4e/0xee0 [snd_pcm]

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&group->lock);
  lock(&group->lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by pulseaudio/4180:
 #0: ffffffffa1a05190 (snd_pcm_link_rwsem){++++}-{3:3}, at: snd_pcm_common_ioctl+0xca0/0xee0 [snd_pcm]
 #1: ffff8883f7a8cf18 (&group->lock){-...}-{2:2}, at: snd_pcm_common_ioctl+0xe4e/0xee0 [snd_pcm]
[...]

Cc: stable@vger.kernel.org
Fixes: f57f3df0 ("ALSA: pcm: More fine-grained PCM link locking")
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Link: https://lore.kernel.org/r/37252c65941e58473b1219ca9fab03d48f47e3e3.1591610330.git.mirq-linux@rere.qmqm.pl



Signed-off-by: Takashi Iwai <tiwai@suse.de>

parent e4b0e41f

sound/core/pcm_native.c

+12 −2

Original line number	Diff line number	Diff line
		@@ -138,6 +138,16 @@ void snd_pcm_stream_lock_irq(struct snd_pcm_substream *substream)
		}
		EXPORT_SYMBOL_GPL(snd_pcm_stream_lock_irq);

		static void snd_pcm_stream_lock_nested(struct snd_pcm_substream *substream)
		{
		struct snd_pcm_group *group = &substream->self_group;

		if (substream->pcm->nonatomic)
		mutex_lock_nested(&group->mutex, SINGLE_DEPTH_NESTING);
		else
		spin_lock_nested(&group->lock, SINGLE_DEPTH_NESTING);
		}

		/**
		* snd_pcm_stream_unlock_irq - Unlock the PCM stream
		* @substream: PCM substream
		@@ -2194,7 +2204,7 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
		snd_pcm_stream_unlock_irq(substream);

		snd_pcm_group_lock_irq(target_group, nonatomic);
		snd_pcm_stream_lock(substream1);
		snd_pcm_stream_lock_nested(substream1);
		snd_pcm_group_assign(substream1, target_group);
		refcount_inc(&target_group->refs);
		snd_pcm_stream_unlock(substream1);
		@@ -2210,7 +2220,7 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)

		static void relink_to_local(struct snd_pcm_substream *substream)
		{
		snd_pcm_stream_lock(substream);
		snd_pcm_stream_lock_nested(substream);
		snd_pcm_group_assign(substream, &substream->self_group);
		snd_pcm_stream_unlock(substream);
		}

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