linux-kernel - Re: [PATCH 07/10] module: _

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Message-ID: <20100224221749.GI6980@linux.vnet.ibm.com>
Date:	Wed, 24 Feb 2010 14:17:49 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com
Subject: Re: [PATCH 07/10] module: __rcu annotations

On Wed, Feb 24, 2010 at 09:26:09PM +0100, Arnd Bergmann wrote:
> On Wednesday 24 February 2010, Alexey Dobriyan wrote:
> > On Wed, Feb 24, 2010 at 09:04:03PM +0100, Arnd Bergmann wrote:
> > > @@ -360,10 +360,12 @@ struct module *find_module(const char *name)
> > >  {
> > >       struct module *mod;
> > >  
> > > -     list_for_each_entry(mod, &modules, list) {
> > > +     rcu_read_lock();
> > > +     list_for_each_entry_rcu(mod, &modules, list) {
> > >               if (strcmp(mod->name, name) == 0)
> > >                       return mod;
> > >       }
> > > +     rcu_read_unlock();
> > >       return NULL;
> > >  }
> > >  EXPORT_SYMBOL_GPL(find_module);
> > 
> > modules list is under module_mutex, nothing should be done here.
> 
> Ok, this is a significant limitation of the list rcu annotation
> then, it's not possible to pass the same list into list_for_each_entry
> and list_for_each_entry_rcu with the way I changed the rcu list
> definition. I would be possible to do a __list_for_each_entry_rcu
> macro that takes an rcu_list_head but does not actually use
> rcu_dereference, but I'm not sure if that's good enough.

Hmmm...  If the __rcu annotation was visible at runtime, it would be
easy provide an annotated version of list_for_each_entry_rcu() that
checks for module_mutex being held under lockdep.

							Thanx, Paul
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