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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>
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@ -69,8 +69,17 @@ int sdw_bus_master_add(struct sdw_bus *bus, struct device *parent,
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return -EINVAL;
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}
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mutex_init(&bus->msg_lock);
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mutex_init(&bus->bus_lock);
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/*
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* Give each bus_lock and msg_lock a unique key so that lockdep won't
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* trigger a deadlock warning when the locks of several buses are
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* grabbed during configuration of a multi-bus stream.
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*/
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lockdep_register_key(&bus->msg_lock_key);
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__mutex_init(&bus->msg_lock, "msg_lock", &bus->msg_lock_key);
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lockdep_register_key(&bus->bus_lock_key);
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__mutex_init(&bus->bus_lock, "bus_lock", &bus->bus_lock_key);
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INIT_LIST_HEAD(&bus->slaves);
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INIT_LIST_HEAD(&bus->m_rt_list);
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@ -181,6 +190,8 @@ void sdw_bus_master_delete(struct sdw_bus *bus)
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sdw_master_device_del(bus);
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sdw_bus_debugfs_exit(bus);
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lockdep_unregister_key(&bus->bus_lock_key);
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lockdep_unregister_key(&bus->msg_lock_key);
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ida_free(&sdw_bus_ida, bus->id);
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}
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EXPORT_SYMBOL(sdw_bus_master_delete);
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@ -5,6 +5,7 @@
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#define __SOUNDWIRE_H
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#include <linux/bug.h>
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#include <linux/lockdep_types.h>
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#include <linux/mod_devicetable.h>
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#include <linux/bitfield.h>
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@ -907,7 +908,9 @@ struct sdw_bus {
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struct list_head slaves;
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DECLARE_BITMAP(assigned, SDW_MAX_DEVICES);
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struct mutex bus_lock;
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struct lock_class_key bus_lock_key;
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struct mutex msg_lock;
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struct lock_class_key msg_lock_key;
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int (*compute_params)(struct sdw_bus *bus);
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const struct sdw_master_ops *ops;
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const struct sdw_master_port_ops *port_ops;
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