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Date: Thu, 23 Sep 2010 13:09:28 -0400
From: Mathieu Desnoyers <compudj@krystal.dyndns.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Jason Baron <jbaron@redhat.com>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Andi Kleen <andi@firstfloor.org>, David Miller <davem@davemloft.net>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [PATCH 03/11] jump label: Base patch for jump label
Message-ID: <20100923170928.GB20365@Krystal>
References: <20100923034910.867858597@goodmis.org> <20100923035608.228041459@goodmis.org> <20100923143758.GA4022@Krystal> <20100923153902.GD2825@redhat.com> <1285260731.26872.1436.camel@gandalf.stny.rr.com>
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* Steven Rostedt (rostedt@goodmis.org) wrote:
> On Thu, 2010-09-23 at 11:39 -0400, Jason Baron wrote:
> > On Thu, Sep 23, 2010 at 10:37:58AM -0400, Mathieu Desnoyers wrote:
> 
> > I was thinking about the rcu_read_lock/synchronize_rcu() for this race.
> > We can hold the rcu_read_lock() across the is_module_text_address()
> > check in the jump label code, and then we can do in module.c:
> > 
> > mod->module_init = NULL;
> > synchronize_rcu();
> > module_free(mod, mod->module_init);
> 
> Um, isn't that last call the same as:
> 
> 	module_free(mod, NULL); ?

Yes, this is incorrect (as I pointed out in my reply). We should do,
instead:

module_init = mod->module_init;
mod->module_init = NULL;
synchronize_rcu();
module_free(mod, module_init);

Thanks,

Mathieu

> 
> I'll spend some time looking at this too.
> 
> -- Steve
> 
> > .
> > .
> > .
> > 
> > or we could push the rcu_read_lock() further down into
> > is_module_address()?
> > 
> > thanks,
> > 
> > -Jason
> > 
> 
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com