linux-kernel - [PATCH 4.2.y-ckt 301/305] ASoC: Use nested lock for snd_soc_dapm_mutex

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Message-Id: <1452902519-2754-302-git-send-email-kamal@canonical.com>
Date:	Fri, 15 Jan 2016 16:01:55 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>,
	Mark Brown <broonie@...nel.org>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 301/305] ASoC: Use nested lock for snd_soc_dapm_mutex_lock

4.2.8-ckt2 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>

commit 783513eec3209542fcd6ac0cbcb030b3c17a4827 upstream.

snd_soc_dapm_mutex_lock currently uses the un-nested call which can
cause lockdep warnings when called from control handlers (a relatively
common usage) and using modules. As creating the control causes a
potential mutex inversion with the handler, creating the control will
take the controls_rwsem under the dapm_mutex and accessing the control
will take the dapm_mutex under controls_rwsem.

All the users look like they want to be using the runtime class of the
lock anyway, so this patch just changes snd_soc_dapm_mutex_lock to use
the nested call, with the SND_SOC_DAPM_CLASS_RUNTIME class.

Fixes: f6d5e586b416 ("ASoC: dapm: Add helpers to lock/unlock DAPM mutex")
Signed-off-by: Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@...nel.org>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 include/sound/soc.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/sound/soc.h b/include/sound/soc.h
index 334d0d2..78a58c1 100644
--- a/include/sound/soc.h
+++ b/include/sound/soc.h
@@ -1629,7 +1629,7 @@ extern const struct dev_pm_ops snd_soc_pm_ops;
 /* Helper functions */
 static inline void snd_soc_dapm_mutex_lock(struct snd_soc_dapm_context *dapm)
 {
-	mutex_lock(&dapm->card->dapm_mutex);
+	mutex_lock_nested(&dapm->card->dapm_mutex, SND_SOC_DAPM_CLASS_RUNTIME);
 }

 static inline void snd_soc_dapm_mutex_unlock(struct snd_soc_dapm_context *dapm)
-- 
1.9.1