Messages in this thread | | | Subject | Re: Virtual device and ARP table | From | Eric Dumazet <> | Date | Mon, 07 Jun 2010 14:22:00 +0200 |
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Le lundi 07 juin 2010 à 12:21 +0200, Christophe Jelger a écrit : > Hello, > > I am currently "resurrecting" a Linux module (called LUNAR) which I > co-developed in 2007 and I'm having a weird kernel crash. This code > basically used to work fine up to 2.6.18 which was the latest version > before we stopped our development. I quickly ported it to 2.6.{31,32}: > it compiles fine and loads fine, but it crashes/hangs the kernel when > it's really being used. > > The module is a virtual device used for MANET routing: with the current > version, it basically "captures" DNS requests sent to the virtual > interface --> this triggers the sending of a fake DNS reply (see below) > and the creation of an ARP table entry for the destination (the MANET > route is built at the same time). Packets can then be sent to the > destination. > > The problem I'm having is that the kernel quickly hangs after I create a > new ARP entry (actually only if it's being used). If the entry I create > is set to NUD_PERMANENT, then everything works fine! I use > __neigh_lookup_errno to lookup/create the entry and neigh_lookup to > set/update the MAC address. Note that the ARP entry is created without > problem, but typically even just doing a userspace "arp -a" command can > crash the kernel (it also hangs the userspace command!). Doing "arp -na" > usually does NOT crash the kernel! > > I guess the problem comes from a combination of ARP + DNS > lookups/replies. Note that my kernel module has its own internal fake > DNS server which captures lookups and sends replies directly back to the > stack. What is amazing: if the ARP entry I create is set to > NUD_PERMANENT, then I don't get any crash (however I cannot develop my > module with permanent ARP entries). > > I'm wondering if there were any major changes to the neighbor and arp > code (between 2.6.18 and 2.6.31) that are somehow causing this problem ?... > > Any hint is very welcome. > > thanks in advance, > Christophe > > PS: I can easily reproduce the problem, and was trying to debug with > qemu and gdb server but so fra no success to clearly identify the > problem. Last point: it seems the kernel does not really "crash" but > rather ends up in some unstable state and maybe in a loop. > --
Hi Christophe
You should ask these kind of questions on netdev instead of lkml.
And of course, post your patch, or send us a crystal ball ;)
Yes, many things changed between 2.6.18 and 2.6.34
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