device-core: Kill the lockdep_mutex

Per Peter [1], the lockdep API has native support for all the use cases
lockdep_mutex was attempting to enable. Now that all lockdep_mutex users
have been converted to those APIs, drop this lock.

Link: https://lore.kernel.org/r/Ylf0dewci8myLvoW@hirez.programming.kicks-ass.net [1]
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/165055522548.3745911.14298368286915484086.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/base/core.c

@@ -2864,9 +2864,6 @@ void device_initialize(struct device *dev)
 	kobject_init(&dev->kobj, &device_ktype);
 	INIT_LIST_HEAD(&dev->dma_pools);
 	mutex_init(&dev->mutex);
-#ifdef CONFIG_PROVE_LOCKING
-	mutex_init(&dev->lockdep_mutex);
-#endif
 	lockdep_set_novalidate_class(&dev->mutex);
 	spin_lock_init(&dev->devres_lock);
 	INIT_LIST_HEAD(&dev->devres_head);

include/linux/device.h

@@ -400,8 +400,6 @@ struct dev_msi_info {
  * 		This identifies the device type and carries type-specific
  * 		information.
  * @mutex:	Mutex to synchronize calls to its driver.
- * @lockdep_mutex: An optional debug lock that a subsystem can use as a
- * 		peer lock to gain localized lockdep coverage of the device_lock.
  * @bus:	Type of bus device is on.
  * @driver:	Which driver has allocated this
  * @platform_data: Platform data specific to the device.
@@ -499,9 +497,6 @@ struct device {
 					   core doesn't touch it */
 	void		*driver_data;	/* Driver data, set and get with
 					   dev_set_drvdata/dev_get_drvdata */
-#ifdef CONFIG_PROVE_LOCKING
-	struct mutex		lockdep_mutex;
-#endif
 	struct mutex		mutex;	/* mutex to synchronize calls to
 					 * its driver.
 					 */