soundwire: bus: Prevent lockdep asserts when stream has multiple buses

Give the bus_lock and msg_lock of each bus a different unique key
so that it is possible to acquire the locks of multiple buses
without lockdep asserting a possible deadlock.

Using mutex_init() to initialize a mutex gives all those mutexes
the same lock class. Lockdep checking treats it as an error to
attempt to take a mutex while already holding a mutex of the same
class. This causes a lockdep assert when sdw_acquire_bus_lock()
attempts to lock multiple buses, and when do_bank_switch() takes
multiple msg_lock.

[  138.697350] WARNING: possible recursive locking detected
[  138.697366] 6.3.0-test #1 Tainted: G            E
[  138.697380] --------------------------------------------
[  138.697394] play/903 is trying to acquire lock:
[  138.697409] ffff99b8c41aa8c8 (&bus->bus_lock){+.+.}-{3:3}, at:
sdw_prepare_stream+0x52/0x2e0
[  138.697443]
               but task is already holding lock:
[  138.697468] ffff99b8c41af8c8 (&bus->bus_lock){+.+.}-{3:3}, at:
sdw_prepare_stream+0x52/0x2e0
[  138.697493]
               other info that might help us debug this:
[  138.697521]  Possible unsafe locking scenario:

[  138.697540]        CPU0
[  138.697550]        ----
[  138.697559]   lock(&bus->bus_lock);
[  138.697570]   lock(&bus->bus_lock);
[  138.697581]
                *** DEADLOCK ***

Giving each mutex a unique key allows multiple to be held
without triggering a lockdep assert. But note that it does not
allow them to be taken in one order then a different order.
If two mutexes are taken in the order A, B then they must
always be taken in that order otherwise they could deadlock.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20230615141208.679011-1-rf@opensource.cirrus.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/soundwire/sdw.h b/include/linux/soundwire/sdw.h
index c076a3f879b3..f523ceabd059 100644
--- a/include/linux/soundwire/sdw.h
+++ b/include/linux/soundwire/sdw.h
@@ -5,6 +5,7 @@
 #define __SOUNDWIRE_H
 
 #include <linux/bug.h>
+#include <linux/lockdep_types.h>
 #include <linux/mod_devicetable.h>
 #include <linux/bitfield.h>
 
@@ -907,7 +908,9 @@ struct sdw_bus {
 	struct list_head slaves;
 	DECLARE_BITMAP(assigned, SDW_MAX_DEVICES);
 	struct mutex bus_lock;
+	struct lock_class_key bus_lock_key;
 	struct mutex msg_lock;
+	struct lock_class_key msg_lock_key;
 	int (*compute_params)(struct sdw_bus *bus);
 	const struct sdw_master_ops *ops;
 	const struct sdw_master_port_ops *port_ops;