Re: [PATCH 1/2] module: use rcu to protect module list read

[Cong Wang]

On 03/13/2012 08:37 AM, Rusty Russell wrote:
> On Sat, 10 Mar 2012 07:25:57 -0800, Eric Dumazet<eric.dumazet@xxxxxxxxx>  wrote:
> > Le samedi 10 mars 2012 Ã 22:20 +0800, Cong Wang a Ãcrit :
> > > Now the read of module list is protected by preempt disable + *_rcu
> > > list operations, this is odd, as RCU read lock should be able to
> > > protect it directly. This patch makes the read of module list
> > > protected by RCU read lock and the write still protected by
> > > module_mutex.
> >
> > Problem is that your patch does more than that.
> >
> > In set_all_modules_text_rw() and set_all_modules_text_ro() you removed
> > the mutex in favor of rcu_read_lock()
> >
> > Also, module code uses synchronize_sched(), not synchronize_rcu()
>
> Yes, but only for paranoia.  Really, it's vs. stop_machine().
>
> > Take a look at Documentation/RCU/whatisRCU.txt and see that
> > preempt_disable() / preempt_enable() are documented as a right protect
> > code, in line 333.
> >
> > You added races in /proc/modules as well.
>
> I'm surprised that patch didn't warn... CONFIG_DEBUG_ATOMIC_SLEEP=y
> might help here....

Ok I will enable it for testing.

Thanks.
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