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Subject: Re: [patch 0/9] Fix various __task_cred related invalid RCU
 assumptions
From: Peter Zijlstra <peterz@infradead.org>
To: paulmck@linux.vnet.ibm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
       Thomas Gleixner <tglx@linutronix.de>,
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       James Morris <jmorris@namei.org>, David Howells <dhowells@redhat.com>,
       Andrew Morton <akpm@linux-foundation.org>
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Date: Mon, 14 Dec 2009 15:30:39 +0100
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On Mon, 2009-12-14 at 06:16 -0800, Paul E. McKenney wrote:

> > I think you can use lock_is_held(&rcu_lock_map), except you need to deal
> > with the !debug_locks case, because lockdep stops once debug_locks
> > becomes false, which means lock_is_held() will return rubbish.
> 
> OK, so I need to do something like the following, then?
> 
> 	debug_locks ? lock_is_held(&rcu_lock_map) : 1

Depending on what the safe return value is, yeah. If you want an assert
like function, false is usually the safe one.

#define lockdep_assert_held(l)  WARN_ON(debug_locks && !lockdep_is_held(l))

is the one in-tree user of this.