[PATCH 1/4] lockdep: lock_set_subclass() fix

[Yong Zhang]

Since commit f59de89 [lockdep: Clear whole lockdep_map on initialization],
lockdep_init_map() will clear all the struct. But it will break
lock_set_class()/lock_set_subclass(). A typical race condition
is like below:

      CPU A                                   CPU B
lock_set_subclass(lockA);
  lock_set_class(lockA);
    lockdep_init_map(lockA);
      /* lockA->name is cleared */
      memset(lockA);
                                      __lock_acquire(lockA);
                                        /* lockA->class_cache[] is cleared */
                                        register_lock_class(lockA);
                                          look_up_lock_class(lockA);
                                            WARN_ON_ONCE(class->name !=
                                                      lock->name);

      lock->name = name;

Reported-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Reported-by: Borislav Petkov <bp@xxxxxxxxx>
Signed-off-by: Yong Zhang <yong.zhang0@xxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
---
 include/linux/lockdep.h |    2 +-
 kernel/lockdep.c        |    9 +++++----
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index b6a56e3..182fb2d 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -330,7 +330,7 @@ extern void lock_set_class(struct lockdep_map *lock, const char *name,
 static inline void lock_set_subclass(struct lockdep_map *lock,
 		unsigned int subclass, unsigned long ip)
 {
-	lock_set_class(lock, lock->name, lock->key, subclass, ip);
+	lock_set_class(lock, NULL, NULL, subclass, ip);
 }
 
 extern void lockdep_set_current_reclaim_state(gfp_t gfp_mask);
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index e69434b..4a16b0a 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -3247,7 +3247,6 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
 {
 	struct task_struct *curr = current;
 	struct held_lock *hlock, *prev_hlock;
-	struct lock_class *class;
 	unsigned int depth;
 	int i;
 
@@ -3274,9 +3273,11 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
 	return print_unlock_inbalance_bug(curr, lock, ip);
 
 found_it:
-	lockdep_init_map(lock, name, key, 0);
-	class = register_lock_class(lock, subclass, 0);
-	hlock->class_idx = class - lock_classes + 1;
+	/* optimizing for lock_set_subclass() */
+	if (key) {
+		lockdep_init_map(lock, name, key, 0);
+		register_lock_class(lock, subclass, 0);
+	}
 
 	curr->lockdep_depth = i;
 	curr->curr_chain_key = hlock->prev_chain_key;
-- 
1.7.5.4

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