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 --- drivers/soundwire/bus.c | 15 +++++++++++++-- include/linux/soundwire/sdw.h | 3 +++ 2 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c index b44f8d0affa6..dba920ec88f6 100644 --- a/drivers/soundwire/bus.c +++ b/drivers/soundwire/bus.c @@ -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); 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;