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Subject: Re: [PATCH 1/4] lockdep: lock_set_subclass() fix
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Tejun Heo <tj@kernel.org>
Cc: Vegard Nossum <vegard.nossum@gmail.com>,
        Yong Zhang <yong.zhang0@gmail.com>, linux-kernel@vger.kernel.org,
        sergey.senozhatsky@gmail.com, bp@alien8.de,
        Ingo Molnar <mingo@elte.hu>, David Rientjes <rientjes@google.com>,
        casteyde.christian@free.fr
Date: Mon, 07 Nov 2011 17:26:19 +0100
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On Mon, 2011-11-07 at 08:21 -0800, Tejun Heo wrote:

> > @@ -148,9 +148,9 @@ void clear_lock_stats(struct lock_class *class);
> >   * This is embedded into specific lock instances:
> >   */
> >  struct lockdep_map {
> > +	const char			*name;
> >  	struct lock_class_key		*key;
> >  	struct lock_class		*class_cache[NR_LOCKDEP_CACHING_CLASSES];
> > -	const char			*name;
> >  #ifdef CONFIG_LOCK_STAT
> >  	int				cpu;
> >  	unsigned long			ip;
> 
> Probably fat comment explaining the ordering requirement here w/

yes.

> #define LOCKDEP_MAP_INIT_OFFSET		offsetof(struct lockdep_map, class_cache)
> 
> > diff --git a/kernel/lockdep.c b/kernel/lockdep.c
> > index e69434b..81855cf 100644
> > --- a/kernel/lockdep.c
> > +++ b/kernel/lockdep.c
> > @@ -2948,7 +2948,8 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this,
> >  void lockdep_init_map(struct lockdep_map *lock, const char *name,
> >  		      struct lock_class_key *key, int subclass)
> >  {
> > -	memset(lock, 0, sizeof(*lock));
> > +	kmemcheck_mark_initialized(lock, 2*sizeof(void *));
> > +	memset(&lock->class_cache[0], 0, sizeof(*lock)-2*sizeof(void *));
> 
> And something like the following?
> 
> 	memset((void *)lock + LOCKDEP_MAP_INIT_OFFSET, 0,
> 		sizeof(*lock) - LOCKDEP_MAP_INIT_OFFSET);

Much better indeed!