[PATCH 1/2] lockdep: kmemcheck: annotate ->lock in lockdep_init_map()

From: Yong Zhang
Date: Wed Nov 09 2011 - 03:05:19 EST


On Tue, Nov 08, 2011 at 10:40:46AM +0100, Peter Zijlstra wrote:
> On Tue, 2011-11-08 at 17:07 +0800, Yong Zhang wrote:
> > So something like below?
>
> that fails to clear/init the class_cache, leading to all sorts of
> problems.
>
> Wiping the class_cache just reduces performance somewhat, not wiping
> them is disastrous since it can results in wild pointer derefs.
>
> Now we could fix up register_lock_class() to reset the class_cache,
> although that's a little tricky and I'm not sure its worth it.

Yeah, I have done some benchmark which show it's worthful, please
check patch#2.

And below is the one which cure the current problem.

Thanks,
Yong

---
From: Yong Zhang <yong.zhang0@xxxxxxxxx>
Subject: [PATCH 1/2] lockdep: kmemcheck: annotate ->lock in lockdep_init_map()

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;

So restore to what we have done before commit f59de89 but annotate
->lock with kmemcheck_mark_initialized() to suppress the kmemcheck
warning reported in commit f59de89.

Reported-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Reported-by: Borislav Petkov <bp@xxxxxxxxx>
Suggested-by: Vegard Nossum <vegard.nossum@xxxxxxxxx>
Signed-off-by: Yong Zhang <yong.zhang0@xxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
---
kernel/lockdep.c | 7 ++++++-
1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index e69434b..21ea1dc 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -2948,7 +2948,12 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this,
void lockdep_init_map(struct lockdep_map *lock, const char *name,
struct lock_class_key *key, int subclass)
{
- memset(lock, 0, sizeof(*lock));
+ int i;
+
+ kmemcheck_mark_initialized(lock, sizeof(*lock));
+
+ for (i = 0; i < NR_LOCKDEP_CACHING_CLASSES; i++)
+ lock->class_cache[i] = NULL;

#ifdef CONFIG_LOCK_STAT
lock->cpu = raw_smp_processor_id();
--
1.7.5.4

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