Re: [tip:core/urgent] lockdep: Fix wrong assumption inmatch_held_lock

[Yong Zhang]

On Tue, Aug 09, 2011 at 02:30:02PM +0000, tip-bot for Peter Zijlstra wrote:
> Commit-ID:  80e0401e35410a69bfae05b454db8a7187edd6b8
> Gitweb:     http://git.kernel.org/tip/80e0401e35410a69bfae05b454db8a7187edd6b8
> Author:     Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> AuthorDate: Fri, 5 Aug 2011 14:26:17 +0200
> Committer:  Ingo Molnar <mingo@xxxxxxx>
> CommitDate: Tue, 9 Aug 2011 11:57:35 +0200
> 
> lockdep: Fix wrong assumption in match_held_lock
> 
> match_held_lock() was assuming it was being called on a lock class
> that had already seen usage.
> 
> This condition was true for bug-free code using lockdep_assert_held(),
> since you're in fact holding the lock when calling it. However the
> assumption fails the moment you assume the assertion can fail, which
> is the whole point of having the assertion in the first place.
> 
> Anyway, now that there's more lockdep_is_held() users, notably
> __rcu_dereference_check(), its much easier to trigger this since we
> test for a number of locks and we only need to hold any one of them to
> be good.
> 
> Reported-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Link: http://lkml.kernel.org/r/1312547787.28695.2.camel@twins

BTW, I can't open this link.

Thanks,
Yong

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