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[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>
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1 changed files with 6 additions and 0 deletions
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@ -1182,6 +1182,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
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struct lockdep_subclass_key *key;
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struct list_head *hash_head;
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struct lock_class *class;
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unsigned long flags;
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class = look_up_lock_class(lock, subclass);
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if (likely(class))
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@ -1203,6 +1204,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
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key = lock->key->subkeys + subclass;
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hash_head = classhashentry(key);
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raw_local_irq_save(flags);
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__raw_spin_lock(&hash_lock);
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/*
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* We have to do the hash-walk again, to avoid races
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@ -1217,6 +1219,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
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*/
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if (nr_lock_classes >= MAX_LOCKDEP_KEYS) {
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__raw_spin_unlock(&hash_lock);
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raw_local_irq_restore(flags);
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debug_locks_off();
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printk("BUG: MAX_LOCKDEP_KEYS too low!\n");
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printk("turning off the locking correctness validator.\n");
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@ -1239,15 +1242,18 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
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if (verbose(class)) {
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__raw_spin_unlock(&hash_lock);
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raw_local_irq_restore(flags);
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printk("\nnew class %p: %s", class->key, class->name);
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if (class->name_version > 1)
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printk("#%d", class->name_version);
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printk("\n");
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dump_stack();
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raw_local_irq_save(flags);
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__raw_spin_lock(&hash_lock);
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}
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out_unlock_set:
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__raw_spin_unlock(&hash_lock);
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raw_local_irq_restore(flags);
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if (!subclass || force)
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lock->class_cache = class;
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