linux-kernel - Re: mem_cgroup_page_lruvec: BUG: unable to handle kernel NULL pointer dereference at 00000000000001a8

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Date:	Thu, 13 Jun 2013 15:32:44 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Richard Weinberger <richard@....at>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	cgroups mailinglist <cgroups@...r.kernel.org>,
	"kamezawa.hiroyu@...fujitsu.com" <kamezawa.hiroyu@...fujitsu.com>,
	bsingharora@...il.com, hannes@...xchg.org
Subject: Re: mem_cgroup_page_lruvec: BUG: unable to handle kernel NULL
 pointer dereference at 00000000000001a8

Ohh and could you post the config please? Sorry should have asked
earlier.

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
> 
> >   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.
> 
> Is this easily reproducible? Could you configure kdump.

-- 
Michal Hocko
SUSE Labs
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