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Subject[PATCH 1/4] lockdep: lock_set_subclass() fix
Date
Since commit f59de89 [lockdep: Clear whole lockdep_map on initialization],
lockdep_init_map() will clear all the struct. But it will break
lock_set_class()/lock_set_subclass(). A typical race condition
is like below:

CPU A CPU B
lock_set_subclass(lockA);
lock_set_class(lockA);
lockdep_init_map(lockA);
/* lockA->name is cleared */
memset(lockA);
__lock_acquire(lockA);
/* lockA->class_cache[] is cleared */
register_lock_class(lockA);
look_up_lock_class(lockA);
WARN_ON_ONCE(class->name !=
lock->name);
lock->name = name;

Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Tejun Heo <tj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
---
include/linux/lockdep.h | 2 +-
kernel/lockdep.c | 9 +++++----
2 files changed, 6 insertions(+), 5 deletions(-)
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index b6a56e3..182fb2d 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -330,7 +330,7 @@ extern void lock_set_class(struct lockdep_map *lock, const char *name,
static inline void lock_set_subclass(struct lockdep_map *lock,
unsigned int subclass, unsigned long ip)
{
- lock_set_class(lock, lock->name, lock->key, subclass, ip);
+ lock_set_class(lock, NULL, NULL, subclass, ip);
}

extern void lockdep_set_current_reclaim_state(gfp_t gfp_mask);
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index e69434b..4a16b0a 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -3247,7 +3247,6 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
{
struct task_struct *curr = current;
struct held_lock *hlock, *prev_hlock;
- struct lock_class *class;
unsigned int depth;
int i;

@@ -3274,9 +3273,11 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
return print_unlock_inbalance_bug(curr, lock, ip);

found_it:
- lockdep_init_map(lock, name, key, 0);
- class = register_lock_class(lock, subclass, 0);
- hlock->class_idx = class - lock_classes + 1;
+ /* optimizing for lock_set_subclass() */
+ if (key) {
+ lockdep_init_map(lock, name, key, 0);
+ register_lock_class(lock, subclass, 0);
+ }

curr->lockdep_depth = i;
curr->curr_chain_key = hlock->prev_chain_key;
--
1.7.5.4


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