[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>

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 3926c367435457553c419aab736ee68803761ab0..62e73ce681972ad350cda5b50037ab30c381c67a 100644 (file)
--- 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;