2 files changed, 30 insertions, 8 deletions

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 06aed8305bf3..2186a64ee4b5 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -32,6 +32,17 @@ extern int lock_stat;
 #define MAX_LOCKDEP_SUBCLASSES          8UL
 
 /*
+ * NR_LOCKDEP_CACHING_CLASSES ... Number of classes
+ * cached in the instance of lockdep_map
+ *
+ * Currently main class (subclass == 0) and signle depth subclass
+ * are cached in lockdep_map. This optimization is mainly targeting
+ * on rq->lock. double_rq_lock() acquires this highly competitive with
+ * single depth.
+ */
+#define NR_LOCKDEP_CACHING_CLASSES      2
+
+/*
  * Lock-classes are keyed via unique addresses, by embedding the
  * lockclass-key into the kernel (or module) .data section. (For
  * static locks we use the lock address itself as the key.)
@@ -138,7 +149,7 @@ void clear_lock_stats(struct lock_class *class);
  */
 struct lockdep_map {
         struct lock_class_key           *key;
-        struct lock_class               *class_cache;
+        struct lock_class               *class_cache[NR_LOCKDEP_CACHING_CLASSES];
         const char                      *name;
 #ifdef CONFIG_LOCK_STAT
         int                             cpu;
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 84baa71cfda5..bc4d32871f9a 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -774,7 +774,9 @@ out_unlock_set:
         raw_local_irq_restore(flags);
 
         if (!subclass || force)
-                lock->class_cache = class;
+                lock->class_cache[0] = class;
+        else if (subclass < NR_LOCKDEP_CACHING_CLASSES)
+                lock->class_cache[subclass] = class;
 
         if (DEBUG_LOCKS_WARN_ON(class->subclass != subclass))
                 return NULL;
@@ -2679,7 +2681,11 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this,
 void lockdep_init_map(struct lockdep_map *lock, const char *name,
                       struct lock_class_key *key, int subclass)
 {
-        lock->class_cache = NULL;
+        int i;
+
+        for (i = 0; i < NR_LOCKDEP_CACHING_CLASSES; i++)
+                lock->class_cache[i] = NULL;
+
 #ifdef CONFIG_LOCK_STAT
         lock->cpu = raw_smp_processor_id();
 #endif
@@ -2750,10 +2756,10 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
         if (lock->key == &__lockdep_no_validate__)
                 check = 1;
 
-        if (!subclass)
-                class = lock->class_cache;
+        if (subclass < NR_LOCKDEP_CACHING_CLASSES)
+                class = lock->class_cache[subclass];
         /*
-         * Not cached yet or subclass?
+         * Not cached?
          */
         if (unlikely(!class)) {
                 class = register_lock_class(lock, subclass, 0);
@@ -2918,7 +2924,7 @@ static int match_held_lock(struct held_lock *hlock, struct lockdep_map *lock)
                 return 1;
 
         if (hlock->references) {
-                struct lock_class *class = lock->class_cache;
+                struct lock_class *class = lock->class_cache[0];
 
                 if (!class)
                         class = look_up_lock_class(lock, 0);
@@ -3559,7 +3565,12 @@ void lockdep_reset_lock(struct lockdep_map *lock)
                 if (list_empty(head))
                         continue;
                 list_for_each_entry_safe(class, next, head, hash_entry) {
-                        if (unlikely(class == lock->class_cache)) {
+                        int match = 0;
+
+                        for (j = 0; j < NR_LOCKDEP_CACHING_CLASSES; j++)
+                                match |= class == lock->class_cache[j];
+
+                        if (unlikely(match)) {
                                 if (debug_locks_off_graph_unlock())
                                         WARN_ON(1);
                                 goto out_restore;