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Date: Thu, 3 Nov 2011 15:27:05 +0800
From: Yong Zhang <yong.zhang0@gmail.com>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: David Rientjes <rientjes@google.com>, Tejun Heo <tj@kernel.org>,
        Ingo Molnar <mingo@elte.hu>, Borislav Petkov <bp@alien8.de>,
        Peter Zijlstra <peterz@infradead.org>, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: WARNING: at kernel/lockdep.c:690 __lock_acquire+0x168/0x164b()
Message-ID: <20111103072705.GA15871@zhy>
Reply-To: Yong Zhang <yong.zhang0@gmail.com>
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On Thu, Nov 03, 2011 at 10:17:36AM +0300, Sergey Senozhatsky wrote:
> On (10/21/11 17:45), Yong Zhang wrote:
> > On Fri, Oct 21, 2011 at 02:14:34AM -0700, David Rientjes wrote:
> > > How does it mask the race condition?  Before the memset(), the ->name 
> > > field was never _cleared_ in lockdep_init_map() like it is now, it was 
> > > only stored.
> > 
> > A typcal race condition will like this:
> > 
> > 	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;
> > 
> > And a untested patch is below:
> > BTW, now the patch could cure (I guess) the very issue reported
> > in this thread.
> > But it don't cover the case which change the key and the relevant
> > lock_class has existed, I don't think out a way how to fix it yet :)
> > But the fact is we have no such caller yet, the only call site of
> > lock_set_subclass() is double_unlock_balance().
> > 
> 
> Hello,
> Any news on this patch? Do you like it or hate it? With recent kernels
> I'm able to hit this problem more often (several time a day) so if any
> testing is required I'm willing to help.

Did you have tried it? Though I don't find time to polish it yet but
I think will smooth your concern.

Thanks,
Yong