Re: [PATCH 03/10] mac80211: Use rcu_barrier() on unload.

[Johannes Berg]

On Wed, 2009-06-24 at 12:06 +0200, Jesper Dangaard Brouer wrote:
> On Tue, 2009-06-23 at 17:15 +0200, Johannes Berg wrote:
> > On Tue, 2009-06-23 at 17:04 +0200, Jesper Dangaard Brouer wrote:
> > > The mac80211 module uses rcu_call() thus it should use rcu_barrier()
> > > on module unload.
> > > 
> > > I'm having a hardtime verifying that no more call_rcu() callbacks can
> > > be schedules in the module unload path.  Could a maintainer please
> > > look into this?
> > > 
> > > Signed-off-by: Jesper Dangaard Brouer <hawk@xxxxxxx>
> > > ---
> > > 
> > >  net/mac80211/main.c |    2 ++
> > >  1 files changed, 2 insertions(+), 0 deletions(-)
> > > 
> > > diff --git a/net/mac80211/main.c b/net/mac80211/main.c
> > > index 092a017..e9f70ce 100644
> > > --- a/net/mac80211/main.c
> > > +++ b/net/mac80211/main.c
> > > @@ -1100,6 +1100,8 @@ static void __exit ieee80211_exit(void)
> > >  		ieee80211s_stop();
> > >  
> > >  	ieee80211_debugfs_netdev_exit();
> > > +
> > > +	rcu_barrier(); /* Wait for completion of call_rcu()'s */
> > >  }
> > 
> > I don't think this is correct at all -- note that call_rcu() is done in
> > some of the mesh code, so I would think you need to do this in
> > ieee80211_stop() since the call_rcu() code requires the interface to
> > still be around. And when it's stopped everything should be idle.
> 
> Should it then not be in mesh.c ieee80211_stop_mesh().  We can replace
> the synchronize_rcu() in this function with a rcu_barrier().

Yes, this seems correct.

johannes

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