2 files changed, 80 insertions, 13 deletions

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index a6d5e5e4d08..47d42eff612 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -213,10 +213,12 @@ struct held_lock {
          * interrupt context:
          */
         unsigned int irq_context:2; /* bit 0 - soft, bit 1 - hard */
-        unsigned int trylock:1;
+        unsigned int trylock:1;                                         /* 16 bits */
+
         unsigned int read:2;        /* see lock_acquire() comment */
         unsigned int check:2;       /* see lock_acquire() comment */
         unsigned int hardirqs_off:1;
+        unsigned int references:11;                                     /* 32 bits */
 };
 
 /*
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 28914a50991..0bb246e21cd 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -2708,13 +2708,15 @@ EXPORT_SYMBOL_GPL(lockdep_init_map);
  */
 static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
                           int trylock, int read, int check, int hardirqs_off,
-                          struct lockdep_map *nest_lock, unsigned long ip)
+                          struct lockdep_map *nest_lock, unsigned long ip,
+                          int references)
 {
         struct task_struct *curr = current;
         struct lock_class *class = NULL;
         struct held_lock *hlock;
         unsigned int depth, id;
         int chain_head = 0;
+        int class_idx;
         u64 chain_key;
 
         if (!prove_locking)
@@ -2762,10 +2764,24 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
         if (DEBUG_LOCKS_WARN_ON(depth >= MAX_LOCK_DEPTH))
                 return 0;
 
+        class_idx = class - lock_classes + 1;
+
+        if (depth) {
+                hlock = curr->held_locks + depth - 1;
+                if (hlock->class_idx == class_idx && nest_lock) {
+                        if (hlock->references)
+                                hlock->references++;
+                        else
+                                hlock->references = 2;
+
+                        return 1;
+                }
+        }
+
         hlock = curr->held_locks + depth;
         if (DEBUG_LOCKS_WARN_ON(!class))
                 return 0;
-        hlock->class_idx = class - lock_classes + 1;
+        hlock->class_idx = class_idx;
         hlock->acquire_ip = ip;
         hlock->instance = lock;
         hlock->nest_lock = nest_lock;
@@ -2773,6 +2789,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
         hlock->read = read;
         hlock->check = check;
         hlock->hardirqs_off = !!hardirqs_off;
+        hlock->references = references;
 #ifdef CONFIG_LOCK_STAT
         hlock->waittime_stamp = 0;
         hlock->holdtime_stamp = sched_clock();
@@ -2881,6 +2898,30 @@ static int check_unlock(struct task_struct *curr, struct lockdep_map *lock,
         return 1;
 }
 
+static int match_held_lock(struct held_lock *hlock, struct lockdep_map *lock)
+{
+        if (hlock->instance == lock)
+                return 1;
+
+        if (hlock->references) {
+                struct lock_class *class = lock->class_cache;
+
+                if (!class)
+                        class = look_up_lock_class(lock, 0);
+
+                if (DEBUG_LOCKS_WARN_ON(!class))
+                        return 0;
+
+                if (DEBUG_LOCKS_WARN_ON(!hlock->nest_lock))
+                        return 0;
+
+                if (hlock->class_idx == class - lock_classes + 1)
+                        return 1;
+        }
+
+        return 0;
+}
+
 static int
 __lock_set_class(struct lockdep_map *lock, const char *name,
                  struct lock_class_key *key, unsigned int subclass,
@@ -2904,7 +2945,7 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
                  */
                 if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
                         break;
-                if (hlock->instance == lock)
+                if (match_held_lock(hlock, lock))
                         goto found_it;
                 prev_hlock = hlock;
         }
@@ -2923,7 +2964,8 @@ found_it:
                 if (!__lock_acquire(hlock->instance,
                         hlock_class(hlock)->subclass, hlock->trylock,
                                 hlock->read, hlock->check, hlock->hardirqs_off,
-                                hlock->nest_lock, hlock->acquire_ip))
+                                hlock->nest_lock, hlock->acquire_ip,
+                                hlock->references))
                         return 0;
         }
 
@@ -2962,20 +3004,34 @@ lock_release_non_nested(struct task_struct *curr,
                  */
                 if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
                         break;
-                if (hlock->instance == lock)
+                if (match_held_lock(hlock, lock))
                         goto found_it;
                 prev_hlock = hlock;
         }
         return print_unlock_inbalance_bug(curr, lock, ip);
 
 found_it:
-        lock_release_holdtime(hlock);
+        if (hlock->instance == lock)
+                lock_release_holdtime(hlock);
+
+        if (hlock->references) {
+                hlock->references--;
+                if (hlock->references) {
+                        /*
+                         * We had, and after removing one, still have
+                         * references, the current lock stack is still
+                         * valid. We're done!
+                         */
+                        return 1;
+                }
+        }
 
         /*
          * We have the right lock to unlock, 'hlock' points to it.
          * Now we remove it from the stack, and add back the other
          * entries (if any), recalculating the hash along the way:
          */
+
         curr->lockdep_depth = i;
         curr->curr_chain_key = hlock->prev_chain_key;
 
@@ -2984,7 +3040,8 @@ found_it:
                 if (!__lock_acquire(hlock->instance,
                         hlock_class(hlock)->subclass, hlock->trylock,
                                 hlock->read, hlock->check, hlock->hardirqs_off,
-                                hlock->nest_lock, hlock->acquire_ip))
+                                hlock->nest_lock, hlock->acquire_ip,
+                                hlock->references))
                         return 0;
         }
 
@@ -3014,7 +3071,7 @@ static int lock_release_nested(struct task_struct *curr,
         /*
          * Is the unlock non-nested:
          */
-        if (hlock->instance != lock)
+        if (hlock->instance != lock || hlock->references)
                 return lock_release_non_nested(curr, lock, ip);
         curr->lockdep_depth--;
 
@@ -3065,7 +3122,9 @@ static int __lock_is_held(struct lockdep_map *lock)
         int i;
 
         for (i = 0; i < curr->lockdep_depth; i++) {
-                if (curr->held_locks[i].instance == lock)
+                struct held_lock *hlock = curr->held_locks + i;
+
+                if (match_held_lock(hlock, lock))
                         return 1;
         }
 
@@ -3148,7 +3207,7 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 
         current->lockdep_recursion = 1;
         __lock_acquire(lock, subclass, trylock, read, check,
-                       irqs_disabled_flags(flags), nest_lock, ip);
+                       irqs_disabled_flags(flags), nest_lock, ip, 0);
         current->lockdep_recursion = 0;
         raw_local_irq_restore(flags);
 }
@@ -3252,7 +3311,7 @@ __lock_contended(struct lockdep_map *lock, unsigned long ip)
                  */
                 if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
                         break;
-                if (hlock->instance == lock)
+                if (match_held_lock(hlock, lock))
                         goto found_it;
                 prev_hlock = hlock;
         }
@@ -3260,6 +3319,9 @@ __lock_contended(struct lockdep_map *lock, unsigned long ip)
         return;
 
 found_it:
+        if (hlock->instance != lock)
+                return;
+
         hlock->waittime_stamp = sched_clock();
 
         contention_point = lock_point(hlock_class(hlock)->contention_point, ip);
@@ -3299,7 +3361,7 @@ __lock_acquired(struct lockdep_map *lock, unsigned long ip)
                  */
                 if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
                         break;
-                if (hlock->instance == lock)
+                if (match_held_lock(hlock, lock))
                         goto found_it;
                 prev_hlock = hlock;
         }
@@ -3307,6 +3369,9 @@ __lock_acquired(struct lockdep_map *lock, unsigned long ip)
         return;
 
 found_it:
+        if (hlock->instance != lock)
+                return;
+
         cpu = smp_processor_id();
         if (hlock->waittime_stamp) {
                 now = sched_clock();