* Re: Virtual device and ARP table [not found] <4C0CC810.7030501@unibas.ch> @ 2010-06-07 12:22 ` Eric Dumazet 2010-06-07 13:03 ` Christophe Jelger 0 siblings, 1 reply; 4+ messages in thread From: Eric Dumazet @ 2010-06-07 12:22 UTC (permalink / raw) To: Christophe Jelger; +Cc: linux-kernel, netdev 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 ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Virtual device and ARP table 2010-06-07 12:22 ` Virtual device and ARP table Eric Dumazet @ 2010-06-07 13:03 ` Christophe Jelger 2010-06-07 13:30 ` Eric Dumazet 0 siblings, 1 reply; 4+ messages in thread From: Christophe Jelger @ 2010-06-07 13:03 UTC (permalink / raw) To: Eric Dumazet; +Cc: netdev Eric Dumazet wrote: > 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 > Eric: thanks for the forward to the netdev list. Regarding the code, I of course welcome any help but didn't want to pollute the list with unsollicited code: I can of course of course send it directly to anyone who is willing to help (I can easily reproduce the problem on different machines). Christophe ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Virtual device and ARP table 2010-06-07 13:03 ` Christophe Jelger @ 2010-06-07 13:30 ` Eric Dumazet 2010-06-07 14:19 ` [RFC] lunar manet routing module Christophe Jelger 0 siblings, 1 reply; 4+ messages in thread From: Eric Dumazet @ 2010-06-07 13:30 UTC (permalink / raw) To: Christophe Jelger; +Cc: netdev Le lundi 07 juin 2010 à 15:03 +0200, Christophe Jelger a écrit : > > Eric: thanks for the forward to the netdev list. Regarding the code, I > of course welcome any help but didn't want to pollute the list with > unsollicited code: I can of course of course send it directly to anyone > who is willing to help (I can easily reproduce the problem on different > machines). > Christophe, Unless patch is really huge, its ok to send it on netdev, with a RFC label, so that only people with free time take a look, eventually. [RFC] lunar: .... ^ permalink raw reply [flat|nested] 4+ messages in thread
* [RFC] lunar manet routing module 2010-06-07 13:30 ` Eric Dumazet @ 2010-06-07 14:19 ` Christophe Jelger 0 siblings, 0 replies; 4+ messages in thread From: Christophe Jelger @ 2010-06-07 14:19 UTC (permalink / raw) To: Eric Dumazet; +Cc: netdev [-- Attachment #1: Type: text/plain, Size: 809 bytes --] Eric Dumazet wrote: > > Christophe, > > Unless patch is really huge, its ok to send it on netdev, with a RFC > label, so that only people with free time take a look, eventually. > > [RFC] lunar: .... [not sure what 'huge' means, I'm sending 60k -- sorry for the pollution] Eric: thanks for the advice. Instead of a patch I attach a .tgz (hope it's ok) of the module code with a README explaining everything: it compiles for 2.6.31 and 2.6.32, didn't try more recent kernels because I actually want to deploy the whole thing on OpenWRT 2.6.32 on Linksys devices. To all: the lunar module crashes the kernel, so be careful. I tried debugging with qemu and gdb server but could not find the bug(s) -- my experience for kernel debugging is in fact limited. thanks in advance for any help, Christophe [-- Attachment #2: lunar.tgz --] [-- Type: application/x-compressed-tar, Size: 59498 bytes --] ^ permalink raw reply [flat|nested] 4+ messages in thread
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2010-06-07 12:22 ` Virtual device and ARP table Eric Dumazet
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2010-06-07 13:30 ` Eric Dumazet
2010-06-07 14:19 ` [RFC] lunar manet routing module Christophe Jelger
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