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

Jesper Dangaard Brouer
2009-06-08T13:11:23Z

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