linux-kernel - Re: [patch 0/9] Fix various __task_cred related invalid RCU assumptions

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Message-ID: <20091215012322.GI6679@linux.vnet.ibm.com>
Date:	Mon, 14 Dec 2009 17:23:22 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>, Oleg Nesterov <oleg@...sign.ru>,
	Al Viro <viro@...iv.linux.org.uk>,
	James Morris <jmorris@...ei.org>,
	David Howells <dhowells@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch 0/9] Fix various __task_cred related invalid RCU
	assumptions

On Mon, Dec 14, 2009 at 03:30:39PM +0100, Peter Zijlstra wrote:
> 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.

Sounds good, thank you for the tip!!!

							Thanx, Paul
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