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

Jesper Dangaard Brouer
2009-06-24T10:06:24Z

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@comx.dk>
> > ---
> >
> > 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().

> I can fix it later, but I'm deep in some other stuff right now.

Yes, I noticed you seem quite active :-)
I can also do a repost... what about the patch below?

--
Med venlig hilsen / Best regards
Jesper Brouer
ComX Networks A/S
Linux Network developer
Cand. Scient Datalog / MSc.
Author of http://adsl-optimizer.dk
LinkedIn: http://www.linkedin.com/in/brouer

[PATCH v2 03/10] mac80211: Use rcu_barrier() on unload.

From: Jesper Dangaard Brouer <hawk@comx.dk>

The mac80211 module uses rcu_call() thus it should use rcu_barrier()
on module unload.

The rcu_barrier() is placed in mech.c ieee80211_stop_mesh() which is
invoked from ieee80211_stop() in case vif.type == NL80211_IFTYPE_MESH_POINT.

Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk>
---

net/mac80211/mesh.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/net/mac80211/mesh.c b/net/mac80211/mesh.c
index fc712e6..11cf45b 100644
--- a/net/mac80211/mesh.c
+++ b/net/mac80211/mesh.c
@@ -494,7 +494,7 @@ void ieee80211_stop_mesh(struct ieee80211_sub_if_data *sdata)
* should it be using the interface and enqueuing
* frames at this very time on another CPU.
*/
- synchronize_rcu();
+ rcu_barrier(); /* Wait for RX path and call_rcu()'s */
skb_queue_purge(&sdata->u.mesh.skb_queue);
}