Messages in this thread | | | Date | Mon, 19 Mar 2007 07:19:34 +0200 | From | "Michael S. Tsirkin" <> | Subject | Re: [ofa-general] Re: dst_ifdown breaks infiniband? |
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> Quoting David Miller <davem@davemloft.net>: > Subject: Re: [ofa-general] Re: dst_ifdown breaks infiniband? > > From: "Michael S. Tsirkin" <mst@dev.mellanox.co.il> > Date: Mon, 19 Mar 2007 00:42:34 +0200 > > > > Quoting Michael S. Tsirkin <mst@dev.mellanox.co.il>: > > > Subject: Re: [ofa-general] Re: dst_ifdown breaks infiniband? > > > > > > > Quoting Eric W. Biederman <ebiederman@lnxi.com>: > > > > Subject: Re: [ofa-general] Re: dst_ifdown breaks infiniband? > > > > > > > > "Michael S. Tsirkin" <mst@dev.mellanox.co.il> writes: > > > > > > > > >> > Why is neighbour->dev changed here? > > > > >> > > > > >> It holds reference to device and prevents its destruction. > > > > >> If dst is held somewhere, we cannot destroy the device and deadlock > > > > >> while unregister. > > > > > > > > > > BTW, can this ever happen for the loopback device itself? > > > > > Is it ever unregistered? > > > > > > > > Well I don't think the loopback device is currently but as soon > > > > as we get network namespace support we will have multiple loopback > > > > devices and they will get unregistered when we remove the network > > > > namespace. > > > > > > Hmm. Then the code moving dst->dev to point to the loopback > > > device will have to be fixed too. I'll post a patch a bit later. > > > > Does this look sane (untested)? > > > > Signed-off-by: Michael S. Tsirkin <mst@dev.mellanox.co.il> > > You can't point it at NULL, we don't point it at loopback > just for fun. > > There can be asynchronous paths elsewhere in the networking still > referencing the neigh or dst and they will (correctly) feel free to > derefence whatever device is hanging there. So transitioning > to NULL is invalid. > > You guys will need to come up with a better solution for this silly > situation with network namespaces. Loopback is always available to > point dead routes and neighbour entries at, and this assumption is > massively rooted in the networking.
Yes, I see this now.
I guess it's best to focus on the original problem with dst_ifdown breaking infiniband for now.
For that, we have to audit all the places where dst->neighbour is dereferenced for RCU safety, and this is already a massive task.
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