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[PATCH] lockdep: register_lock_class() fix

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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>
This commit is contained in:
Ingo Molnar 2006-12-06 20:40:50 -08:00 committed by Linus Torvalds
parent 72be2ccfff
commit 70e4506765
1 changed files with 6 additions and 0 deletions
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6
kernel/lockdep.c
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@ -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;