Commit 256a9978 authored by Richard Fitzgerald's avatar Richard Fitzgerald Committed by Vinod Koul
Browse files

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: default avatarRichard Fitzgerald <rf@opensource.cirrus.com>
Reviewed-by: default avatarPierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20230615141208.679011-1-rf@opensource.cirrus.com


Signed-off-by: default avatarVinod Koul <vkoul@kernel.org>
parent 490937d4

drivers/soundwire/bus.c

+13 −2
Original line number Diff line number Diff line
@@ -69,8 +69,17 @@ int sdw_bus_master_add(struct sdw_bus *bus, struct device *parent, 
		return -EINVAL;

	}



	mutex_init(&bus->msg_lock);

	mutex_init(&bus->bus_lock);

	/*

	 * Give each bus_lock and msg_lock a unique key so that lockdep won't

	 * trigger a deadlock warning when the locks of several buses are

	 * grabbed during configuration of a multi-bus stream.

	 */

	lockdep_register_key(&bus->msg_lock_key);

	__mutex_init(&bus->msg_lock, "msg_lock", &bus->msg_lock_key);



	lockdep_register_key(&bus->bus_lock_key);

	__mutex_init(&bus->bus_lock, "bus_lock", &bus->bus_lock_key);



	INIT_LIST_HEAD(&bus->slaves);

	INIT_LIST_HEAD(&bus->m_rt_list);
@@ -181,6 +190,8 @@ void sdw_bus_master_delete(struct sdw_bus *bus) 
	sdw_master_device_del(bus);



	sdw_bus_debugfs_exit(bus);

	lockdep_unregister_key(&bus->bus_lock_key);

	lockdep_unregister_key(&bus->msg_lock_key);

	ida_free(&sdw_bus_ida, bus->id);

}

EXPORT_SYMBOL(sdw_bus_master_delete);

include/linux/soundwire/sdw.h

+3 −0
Original line number Diff line number Diff line
@@ -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;