[Fwd: SUMMARY: KVM+nf_conntrack_htable_size]

[Jon Masters]

On Tue, 2010-02-02 at 14:26 -0500, Jon Masters wrote:
> On Tue, 2010-02-02 at 12:33 -0500, Jon Masters wrote:
> > On Tue, 2010-02-02 at 12:03 -0500, Jon Masters wrote:
> > > On Mon, 2010-02-01 at 10:17 -0500, Kyle McMartin wrote:
> > > > On Sun, Jan 31, 2010 at 04:12:07AM -0500, Jon Masters wrote:
> > > > > The disabling of netfilter on bridges is not really "solving" this
> > > > > problem. The problem is that the hashing code needs fixing. Until that
> > > > > changes, whenever libvirtd plays with namespaces (as it does), we run
> > > > > the risk of falling over as we play with the size of the hashtables.
> > > > > 
> > > > 
> > > > Thanks for the heads up, Jon. I'll watch this and the internal thread
> > > > for a fix.
> > > 
> > > Well, I sent a summary for why it happens. It happens because an IPv6
> > > error (set via icmpv6_error) causes us to set the conntrack (ct) for an
> > > incoming skb to nf_conntrack_untracked (a catchall struct). We then try
> > > to free that like any other conntrack, back into the (now per-namespace)
> > > cache, but it's not a SL[U]B allocated struct, it's a static...boom.
> > > 
> > > The conntrack code should catch this and error it, it should also do
> > > per-namespace cache allocation, and per-namespace hashtable metadata.
> > > I'm *very* surprised if this isn't biting a lot more Fedora users.
> > 
> > Oh, it is. I grabbed the bugs and updated them with a link to the
> > upstream discussion. They're going to add per-namespace untracked ct's
> > in addition to reworking the hashtable bits. I bet there's more
> > aftermath of the "multiple namespace" support left to fix.
> > 
> > https://bugzilla.redhat.com/show_bug.cgi?id=533087
> 
> I updated that bug with a simple hack that will refuse to free the
> untracked conntrack struct if we are so pathologically inclined. With
> that hack, my KVM box is stable and running fine.
> 
> Patrick will do a per-namespace version of the untracked conntrack too,
> to join the per-namespace cachep, hashtable, and other bugs we've found
> as a result of this. Expect an upstream post tomorrow with the patches,
> which should be pulled into Fedora urgently.

http://lkml.org/lkml/2010/2/3/112

Jon.