Re: Kernel 3.7.0-pre-rc1 kernel BUG at drivers/net/xen-netback/netback.c:405 RIP: e030:[<ffffffff814714f9>] [<ffffffff814714f9>] netbk_gop_frag_copy+0x379/0x380

[Konrad Rzeszutek Wilk <konrad@kernel.org>]

On Sat, Oct 06, 2012 at 12:20:54AM +0200, Sander Eikelenboom wrote:
> 
> Friday, October 5, 2012, 9:26:31 PM, you wrote:
> 
> > Sorry for top posting - on mobile.
> 
> > I saw it too yesterday but only on a specific hardware - AMD FX8. What type of CPU do you have?  Does xsave=off on Xen line help?
> 
> Nope the xsave=off doesn't help
> 
> > Sander Eikelenboom <linux@eikelenboom.it> wrote:
> 
> >>Hi Konrad,
> >>
> >>Just tested kernel 3.7.0-pre-rc1 but ran into a oops in netback on boot after starting some guests:
> >>
> >>[  402.723915] ------------[ cut here ]------------
> >>[  402.734629] kernel BUG at drivers/net/xen-netback/netback.c:405!

Looking at the code, this is what we get:

        /* Data must not cross a page boundary. */
        BUG_ON(size + offset > PAGE_SIZE);

Looking at the commits, the one recently added was:
commit c571898ffc24a1768e1b2dabeac0fc7dd4c14601
Author: Andres Lagar-Cavilla <andres@lagarcavilla.org>
Date:   Fri Sep 14 14:26:59 2012 +0000

    xen/gndev: Xen backend support for paged out grant targets V4.
    

But after reverting it and trying the kernel I still got the crash.

So .. the weirdness is that this seems to be only happening on
certain AMD machines - for example on my AMD A8 box I did not see this.

I fear that the next step is to do a bit off git bisection to
get an idea of which merge it might be. I am going to be AFK
on Monday so I won't get to this until Tuesday/Wednesay :-(

.. Thought to help speed this process, this looks like a
candidate:

commit 229993001282e128a49a59ec43d255614775703a
Merge: 7687b80 fd0f586
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon Oct 1 11:13:33 2012 -0700

    Merge branch 'x86-mm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
    
    Pull x86/mm changes from Ingo Molnar:
     "The biggest change is new TLB partial flushing code for AMD CPUs.
      (The v3.6 kernel had the Intel CPU side code, see commits
      e0ba94f14f74..effee4b9b3b.)