Re: mem_cgroup_page_lruvec: BUG: unable to handle kernel NULL pointerdereference at 00000000000001a8

[Richard Weinberger]

Am 13.06.2013 16:45, schrieb Richard Weinberger:
> Am 13.06.2013 16:39, schrieb Michal Hocko:
> > On Thu 13-06-13 15:34:59, Richard Weinberger wrote:
> > > Am 13.06.2013 15:32, schrieb Michal Hocko:
> > > > Ohh and could you post the config please? Sorry should have asked
> > > > earlier.
> > >
> > > See attachment.
> >
> > Nothing unusual there. Could you enable CONFIG_DEBUG_VM maybe it will
> > help too catch the problem earlier.
>
> OK
>
> > > > On Thu 13-06-13 15:29:08, Michal Hocko wrote:
> > > > > On Thu 13-06-13 14:06:20, Richard Weinberger wrote:
> > > > > [...]
> > > > > > All code
> > > > > > ========
> > > > > >     0:   89 50 08                mov    %edx,0x8(%rax)
> > > > > >     3:   48 89 d1                mov    %rdx,%rcx
> > > > > >     6:   0f 1f 40 00             nopl   0x0(%rax)
> > > > > >     a:   49 8b 04 24             mov    (%r12),%rax
> > > > > >     e:   48 89 c2                mov    %rax,%rdx
> > > > > >    11:   48 c1 e8 38             shr    $0x38,%rax
> > > > > >    15:   83 e0 03                and    $0x3,%eax
> > > > >                     nid = page_to_nid
> > > > > >    18:   48 c1 ea 3a             shr    $0x3a,%rdx
> > > > >                     zid = page_zonenum
> >
> > Ohh, I am wrong here. rdx should be nid and eax the zid.
> >
> > > > > >    1c:   48 69 c0 38 01 00 00    imul   $0x138,%rax,%rax
> > > > > >    23:   48 03 84 d1 e0 02 00    add    0x2e0(%rcx,%rdx,8),%rax
> > > > >                     &memcg->nodeinfo[nid]->zoneinfo[zid]
> > > > >
> > > > > >    2a:   00
> > > > > >    2b:*  48 3b 58 70             cmp    0x70(%rax),%rbx     <-- trapping instruction
> > > > >
> > > > > OK, so this maps to:
> > > > >          if (unlikely(lruvec->zone != zone)) <<<
> > > > >                  lruvec->zone = zone;
> > > > >
> > > > > > [35355.883056] RSP: 0000:ffff88003d523aa8  EFLAGS: 00010002
> > > > > > [35355.883056] RAX: 0000000000000138 RBX: ffff88003fffa600 RCX: ffff88003e04a800
> > > > > > [35355.883056] RDX: 0000000000000020 RSI: 0000000000000000 RDI: 0000000000028500
> > > > > > [35355.883056] RBP: ffff88003d523ab8 R08: 0000000000000000 R09: 0000000000000000
> > > > > > [35355.883056] R10: 0000000000000000 R11: dead000000100100 R12: ffffea0000a14000
> > > > > > [35355.883056] R13: ffff88003e04b138 R14: ffff88003d523bb8 R15: ffffea0000a14020
> > > > > > [35355.883056] FS:  0000000000000000(0000) GS:ffff88003fd80000(0000)
> > > > >
> > > > > RAX (lruvec) is obviously incorrect and it doesn't make any sense. rax should
> > > > > contain an address at an offset from ffff88003e04a800 But there is 0x138 there
> > > > > instead.
> >
> > Hmm, now that I am looking at the registers again. RDX which should be
> > nid seems to be quite big. It says this is node 32. Does the machine
> > have really so many NUMA nodes?
>
> No. It's a KVM guest with two CPUs. Nothing special.
> qemu command line:
> qemu-kvm -m 1G -drive file=lxc_host.qcow2,if=virtio -nographic -kernel linux/arch/x86/boot/bzImage -append console=ttyS0 root=/dev/vda2 -net user,hostfwd=tcp::5555-:22 -net
> nic,model=e1000 -smp 4

Errr, I meant four CPUs. :)

Thanks,
//richard

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