[PATCH] lockdep: register_lock_class() fix

The hash_lock must only ever be taken with irqs disabled.  This happens in
all the important places, except one codepath: register_lock_class().  The
race should trigger rarely because register_lock_class() is quite rare and
single-threaded (happens during init most of the time).

The fix is to disable irqs.

( bug found live in -rt: there preemption is alot more agressive and
  preempting with the hash-lock held caused a lockup.)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 3926c3674354..62e73ce68197 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -1182,6 +1182,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
         struct lockdep_subclass_key *key;
         struct list_head *hash_head;
         struct lock_class *class;
+        unsigned long flags;
 
         class = look_up_lock_class(lock, subclass);
         if (likely(class))
@@ -1203,6 +1204,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
         key = lock->key->subkeys + subclass;
         hash_head = classhashentry(key);
 
+        raw_local_irq_save(flags);
         __raw_spin_lock(&hash_lock);
         /*
          * We have to do the hash-walk again, to avoid races
@@ -1217,6 +1219,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
          */
         if (nr_lock_classes >= MAX_LOCKDEP_KEYS) {
                 __raw_spin_unlock(&hash_lock);
+                raw_local_irq_restore(flags);
                 debug_locks_off();
                 printk("BUG: MAX_LOCKDEP_KEYS too low!\n");
                 printk("turning off the locking correctness validator.\n");
@@ -1239,15 +1242,18 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
 
         if (verbose(class)) {
                 __raw_spin_unlock(&hash_lock);
+                raw_local_irq_restore(flags);
                 printk("\nnew class %p: %s", class->key, class->name);
                 if (class->name_version > 1)
                         printk("#%d", class->name_version);
                 printk("\n");
                 dump_stack();
+                raw_local_irq_save(flags);
                 __raw_spin_lock(&hash_lock);
         }
 out_unlock_set:
         __raw_spin_unlock(&hash_lock);
+        raw_local_irq_restore(flags);
 
         if (!subclass || force)
                 lock->class_cache = class;