On Fri, Sep 19, 2014 at 02:06:30PM +0200, Alexander Aring wrote: > On Fri, Sep 19, 2014 at 01:00:02PM +0100, Simon Vincent wrote: > > > > On 19/09/14 12:45, Alexander Aring wrote: > > >On Fri, Sep 19, 2014 at 12:27:54PM +0100, Simon Vincent wrote: > > >>On 19/09/14 12:08, Alexander Aring wrote: > > >>>On Thu, Sep 18, 2014 at 04:19:11PM +0200, Alexander Aring wrote: > > >>>>On Thu, Sep 18, 2014 at 03:02:17PM +0100, Simon Vincent wrote: > > >>>>>I have created a small test program that shows this problem. It looks like a > > >>>>>race condition as sometimes the addresses are not corrupt. > > >>>>> > > >>>>Mhh maybe some used after freed and then we copy somewhere garbage sometimes. > > >>>>Don't know right now. > > >>>> > > >>>>>It looks like if the RAW socket gets the packet before the packet hits the > > >>>>>6lowpan layer the addresses are fine. If the packet hits the 6lowpan layer > > >>>>>before the RAW socket gets the packet then the addresses are corrupt. > > >>>>> > > >>>>>The test program can be found here. > > >>>>>https://github.com/xsilon/sockdebug > > >>>>> > > >>>>>I will continue debugging! > > >>>>> > > >>>>ok, good luck. > > >>>> > > >>>I gave this now a try, how can I see the issue now? > > >>> > > >>>I see on output: > > >>> > > >>>recv_raw_icmp[fe80:0:41:c863:cdab:ffff:bbaa:aaaa%lowpan0->?] > > >>> > > >>>this address doesn't exist in my network. > > >>> > > >>>I can also upload wpan wireshark logs and lowpan wireshark logs, if you > > >>>like. > > >>> > > >>>In sockdebug I changed also "const char* src_string =" to one of my > > >>>lowpan addresses. Simon are you still here to debug this issue with me? > > >>>:-) > > >>Yes this is the same error I am seeing. I find that sometimes the recv > > >>address is correct but mostly you get the corrupt address as the ipv6 header > > >>has been overwritten by our compressed 6lowpan header. > > >> > > >>If you comment out the 6lowpan header compression function it solves the > > >>problem. > > >okay, then I dig now into the issue why the address is garbage. > > > > > >>I am trying to understand how the network stack handles skbs. As it is a > > >>multicast packet it will be sent out on 802.15.4, raw socket and any other > > >>interfaces you have but it looks like in this case the interfaces all get a > > >>skb pointing to the same data. Therefore when we replace the ipv6 header > > >>with a compressed version everyone else still thinks there is a normal ipv6 > > >>header still there and therefore gets corrupt data. Should each interface > > >>get a copy of the data? E.g. the ethernet, wifi, 802.15.4 and raw socket all > > >>get a copy of the skb data not a clone? > > >> > > >>Maybe normally each interface will get a copy of the skb so they can attach > > >>their own mac header but in the case of the RAW socket they don't bother > > >>doing a copy as they don't need to add a header for the socket. But then we > > >>come along and destroy the ipv6 header!! > > >> > > >>Just a theory! > > >> > > >okay, there exists a lot of there. I know what you saying because the > > >data buffer is shared there exist race conditions because some other skb > > >has in the next step a 6LoWPAN header, if I understand that correctly. > > > > > Yes I think the problem is we are sharing the databuffer and modifying the > > contents. We should probably be given a copy of the data buffer. I can't > > find the code that decides if we get a copy or clone of the skb. > > > > yea, IPv6 stack is complicated. :-) > > And if you found it, it would be complicated to make any change on it, > we are only an adapation layer... All 6LoWPAN runtime decisions in IPv6 > are bad and do some change. But the IPv6 are not evil, we can talk with > them that we have something which works on both stacks and doesn't > decrease much the performance of IPv6. If we have something like this > then we have a mainline solution. > mhh, take a look on skb_unshare - make a copy of a shared buffe [0]. Seems that we could use that to have a copy of the buffer. Don't know if this can work, because we are inside of callback and the caller lost the reference then. [0] http://lxr.free-electrons.com/source/include/linux/skbuff.h#L1107 -- To unsubscribe from this list: send the line "unsubscribe linux-wpan" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
