linux-kernel - Re: lockdep oddity

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Message-ID: <20060905193742.GA1566@elte.hu>
Date:	Tue, 5 Sep 2006 21:37:42 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>,
	Daniel Walker <dwalker@...sta.com>,
	Hua Zhong <hzhong@...il.com>
Subject: Re: lockdep oddity


* Ingo Molnar <mingo@...e.hu> wrote:

> * Ingo Molnar <mingo@...e.hu> wrote:
> 
> > > The reason is that the BUILD_LOCK_OPS macros in kernel/lockdep.c 
> > > don't contain any of the *_acquire calls, while all of the _unlock 
> > > functions contain a *_release call. Hence I get immediately 
> > > unbalanced locks.
> > 
> > hmmm ... that sounds like a bug. Weird - i recently ran 
> > PREEMPT+SMP+LOCKDEP kernels and didnt notice this.
> 
> ok, the reason i didnt find this problem is because this is fixed in 
> my tree, but i didnt realize that it's a fix also for upstream ...

actually ... it works fine in the upstream kernel due to this:

  * If lockdep is enabled then we use the non-preemption spin-ops
  * even on CONFIG_PREEMPT, because lockdep assumes that interrupts are
  * not re-enabled during lock-acquire (which the preempt-spin-ops do):
  */
 #if !defined(CONFIG_PREEMPT) || !defined(CONFIG_SMP) || \
         defined(CONFIG_DEBUG_LOCK_ALLOC)

so i'm wondering, how did you you manage to get into the 
BUILD_LOCK_OPS() branch?

	Ingo
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