[PATCH 00/10] We must use rcu_barrier() on module unload

Jesper Dangaard Brouer
2009-06-23T15:04:21Z

This patch series is an attempt to cleanup the entire tree, for
potential oops'es during module unload, due to outstanding RCU
callbacks. (My last rcu_barrier patch series only addressed net/).

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

For documentation see:

Paul E. McKenney's Blog
http://paulmck.livejournal.com/7314.html

http://lwn.net/Articles/217484/

Documentation/RCU/rcubarrier.txt

Looking through the Linux kernel for call_rcu() users and unloadable
modules I found 10 modules that didn't behave correctly.

Please: MAINTAINERS needs to verify that the module exit code prevent
any new RCU callbacks from being posted (before rcu_barrier() is
called). (I have tried to do this verification, but most of these
module are simply too large and complex for me to verify this within
reasonable time)

[Overview description, following patch ordering]

The modules ext4, bridge, mac80211, sunrpc, nfs and ipv6 are fairly
straight forward (maintainers still needs to check for prevent of new
RCU callbacks).

The module decnet, has disabled its module_exit() (since ^1da177e) but
it still seems relevant to keep the code updated.

The modules edac_core and cfq-iosched, has implemented their own
open-coded wait_for_completion() scheme, in order to wait for
call_rcu() calls. Maintainers needs to look into removing this code
and using rcu_barrier() instead.

The module nf_conntrack, has embedded some comments that I would like
Patrick McHardy to look at. As I'm not sure which is are most optimal
place to call rcu_barrier(). The patch probably calls rcu_barrier()
too much, but its a better safe than sorry approach.

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 Linus Torvalds tree (starting on top of
commit f234012f52a3).

Who wants to pickup these patches? (I usually go through DaveM, but
this also touches subsystems that are not (yet?) under DaveM's
maintainer ship)

---
Jesper Dangaard Brouer (10):
nf_conntrack: Use rcu_barrier().
cfq-iosched: Uses its own open-coded rcu_barrier.
edac_core: Uses call_rcu() and its own wait_for_completion scheme.
decnet: Use rcu_barrier() on module unload.
ipv6: Use rcu_barrier() on module unload.
nfs: Use rcu_barrier() on module unload.
sunrpc: Use rcu_barrier() on unload.
mac80211: Use rcu_barrier() on unload.
bridge: Use rcu_barrier() instead of syncronize_net() on unload.
ext4: Use rcu_barrier() on module unload.

block/cfq-iosched.c | 6 ++++++
drivers/edac/edac_device.c | 5 +++++
drivers/edac/edac_mc.c | 5 +++++
drivers/edac/edac_pci.c | 5 +++++
fs/ext4/mballoc.c | 4 +++-
fs/nfs/inode.c | 1 +
net/bridge/br.c | 2 +-
net/decnet/af_decnet.c | 6 ++++++
net/ipv6/af_inet6.c | 2 ++
net/mac80211/main.c | 2 ++
net/netfilter/nf_conntrack_core.c | 5 +++++
net/netfilter/nf_conntrack_standalone.c | 2 ++
net/sunrpc/sunrpc_syms.c | 1 +
13 files changed, 44 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