Subject: [PATCH 0/5] We must use rcu_barrier() on module unload

From: Jesper Dangaard Brouer <[email-masked]>
Date: Mon, 08 Jun 2009 15:11:23 +0200

If an unloadable module uses RCU callbacks, it need to use
rcu_barrier() so that the module may be safely unloaded.

While hacking on a netfilter module of my own, I learned the
importance of calling rcu_barrier() instead of only a
synchronize_rcu() on module unload (iif using any call_rcu()
callbacks).  synchronize_rcu() does wait for a grace period to
elapse, but it does not wait for the callbacks to complete.

For documentation see:
 http://lwn.net/Articles/217484/
 Documentation/RCU/rcubarrier.txt

Looking through the net/ directory for call_rcu() users and unloadable
modules I found 5 modules that didn't behave correctly:

 net/8021q/vlan.c

 net/can/af_can.c

 net/netfilter/nfnetlink_queue.c

 net/sctp/protocol.c

 net/sunrpc/auth_gss/auth_gss.c

I have made a patch for each individual module, so objections can be
made on a per module basis.  I have Cc'ed all of the patches to the
maintainers of each module (according to the MAINTAINERS file).

The patchset is made on top of DaveM's net-next-2.6 tree (starting on
top of commit a1c1db392090). As this is my usual development tree,
even though this patchset is bugfixes. (Just tested it applied cleanly
on Linus'es tree ...)

---
Jesper Dangaard Brouer (5):
      sunrpc/auth_gss: Call rcu_barrier() on module unload.
      sctp: protocol.c call rcu_barrier() on unload.
      can: af_can.c use rcu_barrier() on module unload.
      nfnetlink_queue: Use rcu_barrier() on module unload.
      8021q: Vlan driver should use rcu_barrier() on unload instead of syncronize_net()

 net/8021q/vlan.c                |    2 +-
 net/can/af_can.c                |    2 ++
 net/netfilter/nfnetlink_queue.c |    4 +++-
 net/sctp/protocol.c             |    2 ++
 net/sunrpc/auth_gss/auth_gss.c  |    1 +
 5 files changed, 9 insertions(+), 2 deletions(-)

--
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