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

Paul E. McKenney
2009-06-24T01:44:21Z

On Tue, Jun 23, 2009 at 05:03:53PM +0200, Jesper Dangaard Brouer wrote:
> 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.

These look good from an RCU viewpoint, but I am in no better position
than is Jesper to analyze the individual modules. From an RCU
viewpoint:

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> 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
>