linux-kernel - Re: WARNING: at kernel/lockdep.c:690 __lock

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Date:	Mon, 7 Nov 2011 11:43:16 +0300
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Yong Zhang <yong.zhang0@...il.com>
Cc:	Borislav Petkov <bp@...en8.de>,
	David Rientjes <rientjes@...gle.com>,
	Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: WARNING: at kernel/lockdep.c:690 __lock_acquire+0x168/0x164b()

On (11/07/11 12:54), Yong Zhang wrote:
> > > > Understood. If someone can come up with a simple patch which could
> > > > cover the case I mentioned before, that would be great.
> > > > /me goes to poke at it.
> > > 
> > > I dunno whether this is related but I get the following on 3.1:
> > >
> > 
> > I think this is different problem. Failed check that lockdep key is marked as `static'.
> 
> Actually the lockdep_init_map() in __lock_set_class could lead to
> more problem, such as: certain rq->lock could have different 'key'
> with what we give them in sched_init() because rq is defined staticly.
> 
> Given that, we could have another typical race:
> 
>           CPU A                                   CPU B
>     lock_set_subclass(lockA);
>       lock_set_class(lockA);
>                                             /* lockA->class_cache[] is not set */
>                                             register_lock_class(lockA);
>                                               look_up_lock_class(lockA); /* retrun NULL */
>         lockdep_init_map(lockA);
>           /* lockA->name is cleared */
>           memset(lockA);
>    						if (!static_obj(lock->key))
> 						  /* we get warning here */
>           lock->name = name;
>     
> 
> So memset() in lockdep_init_map() is still the culprit IMHO.
>

Hm, agreed, that still could be the reason.
I guess a little more information may be helpful in some cases.

---
Print key address when attempt to register non-static lock key detected.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

---

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index e69434b..de8a996 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -729,7 +729,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
  	 */
 	if (!static_obj(lock->key)) {
 		debug_locks_off();
-		printk("INFO: trying to register non-static key.\n");
+		printk("INFO: trying to register non-static key at address %p.\n", lock->key);
 		printk("the code is fine but needs lockdep annotation.\n");
 		printk("turning off the locking correctness validator.\n");
 		dump_stack();

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