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:

quoted

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 <redacted>
---

 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 <redacted>

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 <redacted>
---

 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);
 }
 


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