Leanne, Will do. In the absence of kernel.org, please also see the message below, suggesting this is queued for 3.2. Alex ---------- Forwarded Message ---------- Date: 20 September 2011 13:47:55 -0700 From: To: CC: , , , , Subject: [patch for 3.2 1/1] net/netfilter/nf_conntrack_netlink.c: fix Oops on container destroy From: Alex Bligh Subject: net/netfilter/nf_conntrack_netlink.c: fix Oops on container destroy Problem: A repeatable Oops can be caused if a container with networking unshared is destroyed when it has nf_conntrack entries yet to expire. A copy of the oops follows below. A perl program generating the oops repeatably is attached inline below. Analysis: The oops is called from cleanup_net when the namespace is destroyed. conntrack iterates through outstanding events and calls death_by_timeout on each of them, which in turn produces a call to ctnetlink_conntrack_event. This calls nf_netlink_has_listeners, which oopses because net->nfnl is NULL. The perl program generates the container through fork() then clone(NS_NEWNET). I does not explicitly set up netlink explicitly set up netlink, but I presume it was set up else net->nfnl would have been NULL earlier (i.e. when an earlier connection timed out). This would thus suggest that net->nfnl is made NULL during the destruction of the container, which I think is done by nfnetlink_net_exit_batch. I can see that the various subsystems are deinitialised in the opposite order to which the relevant register_pernet_subsys calls are called, and both nf_conntrack and nfnetlink_net_ops register their relevant subsystems. If nfnetlink_net_ops registered later than nfconntrack, then its exit routine would have been called first, which would cause the oops described. I am not sure there is anything to prevent this happening in a container environment. Whilst there's perhaps a more complex problem revolving around ordering of subsystem deinit, it seems to me that missing a netlink event on a container that is dying is not a disaster. An early check for net->nfnl being non-NULL in ctnetlink_conntrack_event appears to fix this. There may remain a potential race condition if it becomes NULL immediately after being checked (I am not sure any lock is held at this point or how synchronisation for subsystem deinitialization works). Patch: The patch attached should apply on everything from 2.6.26 (if not before) onwards; it appears to be a problem on all kernels. This was taken against Ubuntu-3.0.0-11.17 which is very close to 3.0.4. I have torture-tested it with the above perl script for 15 minutes or so; the perl script hung the machine within 20 seconds without this patch. Applicability: If this is the right solution, it should be applied to all stable kernels as well as head. Apart from the minor overhead of checking one variable against NULL, it can never 'do the wrong thing', because if net->nfnl is NULL, an oops will inevitably result. Therefore, checking is a reasonable thing to do unless it can be proven than net->nfnl will never be NULL. Check net->nfnl for NULL in ctnetlink_conntrack_event to avoid Oops on container destroy Signed-off-by: Alex Bligh