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Subject[patch] lockdep: register_lock_class() fix
Subject: [patch] lockdep: register_lock_class() fix
From: Ingo Molnar <mingo@elte.hu>

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>
---
kernel/lockdep.c | 6 ++++++
1 file changed, 6 insertions(+)
Index: linux-mm-genapic.q/kernel/lockdep.c
===================================================================
--- linux-mm-genapic.q.orig/kernel/lockdep.c
+++ linux-mm-genapic.q/kernel/lockdep.c
@@ -1183,6 +1183,7 @@ register_lock_class(struct lockdep_map *
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))
@@ -1204,6 +1205,7 @@ register_lock_class(struct lockdep_map *
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
@@ -1218,6 +1220,7 @@ register_lock_class(struct lockdep_map *
*/
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");
@@ -1240,15 +1243,18 @@ register_lock_class(struct lockdep_map *

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;
-
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