Re: Race between RCU and rmmod

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 2 May 2007 17:30:51 +0530
Dipankar Sarma <dipankar@in.ibm.com> wrote:

> On Wed, May 02, 2007 at 12:50:24PM +0100, David Howells wrote:
> > 
> > Hi Dipankar, Rusty,
> > 
> > I seem to have found a race between RCU and rmmod.  What I see appears to be
> > an RCU destructor function that has a call pending but lives in a module, gets
> > deleted before the RCU callback is processed:
> > 
> > RIP: 0010:[<ffffffff880329b7>]  [<ffffffff880329b7>]
> > 
> > I think that rmmod needs to clear the RCU destructor queue, probably inside of
> > __try_stop_module().
> 
> This is why we have rcu_barrier() although the corresponding documentation
> patch seems to have got dropped. Modules that use RCU must call
> rcu_barrier() in their cleanup routine.
> 

hm, I never knew that.

akpm:/usr/src/linux-2.6.21> grep -r rcu_ drivers | wc -l
182
akpm:/usr/src/linux-2.6.21> grep -r rcu_barrier drivers | wc -l 
0

For a start we should undrop that documentation patch, please.