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Commit 70e45067 authored by Ingo Molnar's avatar Ingo Molnar Committed by Linus Torvalds
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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: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 72be2ccf

kernel/lockdep.c

+6 −0
Original line number Diff line number Diff line
@@ -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;