[PATCH] drivers/core: Replace lockdep_set_novalidate_class() with unique class keys

[Tetsuo Handa]

Commit 1704f47b50b5 ("lockdep: Add novalidate class for dev->mutex
conversion") made it impossible to find real deadlocks unless timing
dependent testings manage to trigger hung task like [1] and [2]. And
lockdep_set_novalidate_class() remained for more than one decade due to
a fear of false positives [3]. But not sharing mutex_init() could make
it possible to find real deadlocks without triggering hung task [4].
Thus, let's assign a unique class key on each "struct device"->mutex.

Link: https://syzkaller.appspot.com/bug?extid=2d6ac90723742279e101 [1]
Link: https://syzkaller.appspot.com/bug?extid=2e39bc6569d281acbcfb [2]
Link: https://lkml.kernel.org/r/Y98FLlr7jkiFlV0k@xxxxxxxxxxxxxxxxxxx [3]
Link: https://lkml.kernel.org/r/827177aa-bb64-87a9-e1af-dfe070744045@xxxxxxxxxxxxxxxxxxx [4]
Suggested-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Co-developed-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Co-developed-by: Hillf Danton <hdanton@xxxxxxxx>
Signed-off-by: Hillf Danton <hdanton@xxxxxxxx>
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
Hello, syzkaller users.

We made a patch that keeps lockdep validation enabled on "struct dev->mutex".
Will you try this patch and see if this patch causes boot failures and/or
too frequent crashes to continue testing.

 drivers/base/core.c      | 7 ++++++-
 include/linux/device.h   | 1 +
 include/linux/lockdep.h  | 6 ++++++
 kernel/locking/lockdep.c | 7 +++++++
 4 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index a3e14143ec0c..c30ecbc4d60e 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -2322,6 +2322,9 @@ static void device_release(struct kobject *kobj)
 	devres_release_all(dev);
 
 	kfree(dev->dma_range_map);
+	mutex_destroy(&dev->mutex);
+	if (!lockdep_static_obj(dev))
+		lockdep_unregister_key(&dev->mutex_key);
 
 	if (dev->release)
 		dev->release(dev);
@@ -2941,7 +2944,9 @@ void device_initialize(struct device *dev)
 	kobject_init(&dev->kobj, &device_ktype);
 	INIT_LIST_HEAD(&dev->dma_pools);
 	mutex_init(&dev->mutex);
-	lockdep_set_novalidate_class(&dev->mutex);
+	if (!lockdep_static_obj(dev))
+		lockdep_register_key(&dev->mutex_key);
+	lockdep_set_class(&dev->mutex, &dev->mutex_key);
 	spin_lock_init(&dev->devres_lock);
 	INIT_LIST_HEAD(&dev->devres_head);
 	device_pm_init(dev);
diff --git a/include/linux/device.h b/include/linux/device.h
index 44e3acae7b36..bdaca9f54dc2 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -570,6 +570,7 @@ struct device {
 	struct mutex		mutex;	/* mutex to synchronize calls to
 					 * its driver.
 					 */
+	struct lock_class_key	mutex_key;	/* Unique key for each device */
 
 	struct dev_links_info	links;
 	struct dev_pm_info	power;
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 1f1099dac3f0..5afc999a7e56 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -172,6 +172,7 @@ do {							\
 	current->lockdep_recursion -= LOCKDEP_OFF;	\
 } while (0)
 
+extern int lockdep_static_obj(const void *obj);
 extern void lockdep_register_key(struct lock_class_key *key);
 extern void lockdep_unregister_key(struct lock_class_key *key);
 
@@ -391,6 +392,11 @@ static inline void lockdep_set_selftest_task(struct task_struct *task)
 # define lockdep_free_key_range(start, size)	do { } while (0)
 # define lockdep_sys_exit() 			do { } while (0)
 
+static inline int lockdep_static_obj(const void *obj)
+{
+	return 0;
+}
+
 static inline void lockdep_register_key(struct lock_class_key *key)
 {
 }
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index e3375bc40dad..74c0113646f1 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -857,6 +857,13 @@ static int static_obj(const void *obj)
 	 */
 	return is_module_address(addr) || is_module_percpu_address(addr);
 }
+
+int lockdep_static_obj(const void *obj)
+{
+	return static_obj(obj);
+}
+EXPORT_SYMBOL_GPL(lockdep_static_obj);
+
 #endif
 
 /*
-- 
2.34.1