linux-kernel - Re: [PATCH 1/4] lockdep: lock_set

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Message-ID: <20111108081433.GA3746@zhy>
Date:	Tue, 8 Nov 2011 16:14:33 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Vegard Nossum <vegard.nossum@...il.com>,
	linux-kernel@...r.kernel.org, sergey.senozhatsky@...il.com,
	bp@...en8.de, Ingo Molnar <mingo@...e.hu>,
	Tejun Heo <tj@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	casteyde.christian@...e.fr
Subject: Re: [PATCH 1/4] lockdep: lock_set_subclass() fix

On Tue, Nov 08, 2011 at 08:56:55AM +0100, Peter Zijlstra wrote:
> On Tue, 2011-11-08 at 10:58 +0800, Yong Zhang wrote:
> > >  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;
> > > 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 *));
> > 
> > That means ->key have chance to be 0 at some time, right? 
> 
> How? We only memset from class_cache onwards, leaving name and key
> untouched.

Hmm, we don't touch key in your patch. My eyes was keeping on ->name.
Sorry.

But how do we deal with ->class_cache? Always set it in
loop_up_lock_class()?

Thanks,
Yong
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