lockdep: lock_set_subclass - reset a held lock's subclass

this can be used to reset a held lock's subclass, for arbitrary-depth
iterated data structures such as trees or lists which have per-node
locks.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 73 insertions, 0 deletions

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 1bfdc30bb0af..f270ce1582ff 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -300,6 +300,9 @@ extern void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 extern void lock_release(struct lockdep_map *lock, int nested,
                          unsigned long ip);
 
+extern void lock_set_subclass(struct lockdep_map *lock, unsigned int subclass,
+                              unsigned long ip);
+
 # define INIT_LOCKDEP                           .lockdep_recursion = 0,
 
 #define lockdep_depth(tsk)      (debug_locks ? (tsk)->lockdep_depth : 0)
@@ -316,6 +319,7 @@ static inline void lockdep_on(void)
 
 # define lock_acquire(l, s, t, r, c, i)         do { } while (0)
 # define lock_release(l, n, i)                  do { } while (0)
+# define lock_set_subclass(l, s, i)             do { } while (0)
 # define lockdep_init()                         do { } while (0)
 # define lockdep_info()                         do { } while (0)
 # define lockdep_init_map(lock, name, key, sub) do { (void)(key); } while (0)
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 6999e64fc248..e14d383dcb0b 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -2660,6 +2660,55 @@ static int check_unlock(struct task_struct *curr, struct lockdep_map *lock,
         return 1;
 }
 
+static int
+__lock_set_subclass(struct lockdep_map *lock,
+                    unsigned int subclass, unsigned long ip)
+{
+        struct task_struct *curr = current;
+        struct held_lock *hlock, *prev_hlock;
+        struct lock_class *class;
+        unsigned int depth;
+        int i;
+
+        depth = curr->lockdep_depth;
+        if (DEBUG_LOCKS_WARN_ON(!depth))
+                return 0;
+
+        prev_hlock = NULL;
+        for (i = depth-1; i >= 0; i--) {
+                hlock = curr->held_locks + i;
+                /*
+                 * We must not cross into another context:
+                 */
+                if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
+                        break;
+                if (hlock->instance == lock)
+                        goto found_it;
+                prev_hlock = hlock;
+        }
+        return print_unlock_inbalance_bug(curr, lock, ip);
+
+found_it:
+        class = register_lock_class(lock, subclass, 0);
+        hlock->class = class;
+
+        curr->lockdep_depth = i;
+        curr->curr_chain_key = hlock->prev_chain_key;
+
+        for (; i < depth; i++) {
+                hlock = curr->held_locks + i;
+                if (!__lock_acquire(hlock->instance,
+                        hlock->class->subclass, hlock->trylock,
+                                hlock->read, hlock->check, hlock->hardirqs_off,
+                                hlock->acquire_ip))
+                        return 0;
+        }
+
+        if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth))
+                return 0;
+        return 1;
+}
+
 /*
  * Remove the lock to the list of currently held locks in a
  * potentially non-nested (out of order) manner. This is a
@@ -2824,6 +2873,26 @@ static void check_flags(unsigned long flags)
 #endif
 }
 
+void
+lock_set_subclass(struct lockdep_map *lock,
+                  unsigned int subclass, unsigned long ip)
+{
+        unsigned long flags;
+
+        if (unlikely(current->lockdep_recursion))
+                return;
+
+        raw_local_irq_save(flags);
+        current->lockdep_recursion = 1;
+        check_flags(flags);
+        if (__lock_set_subclass(lock, subclass, ip))
+                check_chain_key(current);
+        current->lockdep_recursion = 0;
+        raw_local_irq_restore(flags);
+}
+
+EXPORT_SYMBOL_GPL(lock_set_subclass);
+
 /*
  * We are not always called with irqs disabled - do that here,
  * and also avoid lockdep recursion: