WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

[Xen-devel] Possible shadow bug (was: Re: [PATCH] memcg: do not expose u

To: Igor Mammedov <imammedo@xxxxxxxxxx>
Subject: [Xen-devel] Possible shadow bug (was: Re: [PATCH] memcg: do not expose uninitialized mem_cgroup_per_node to world)
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Date: Thu, 9 Jun 2011 13:40:12 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Keir Fraser <keir@xxxxxxx>, Tim Deegan <Tim.Deegan@xxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, "containers@xxxxxxxxxxxxxxxxxxxxxxxxxx" <containers@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Li Zefan <lizf@xxxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, Michal Hocko <mhocko@xxxxxxx>, "linux-mm@xxxxxxxxx" <linux-mm@xxxxxxxxx>, Keir Fraser <keir.xen@xxxxxxxxx>, "akpm@xxxxxxxxxxxxxxxxxxxx" <akpm@xxxxxxxxxxxxxxxxxxxx>, Hiroyuki Kamezawa <kamezawa.hiroyuki@xxxxxxxxx>, Paul Menage <menage@xxxxxxxxxx>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>, "balbir@xxxxxxxxxxxxxxxxxx" <balbir@xxxxxxxxxxxxxxxxxx>
Delivery-date: Thu, 09 Jun 2011 05:37:52 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <4DF0801F.9050908@xxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <1306925044-2828-1-git-send-email-imammedo@xxxxxxxxxx> <20110601123913.GC4266@xxxxxxxxxxxxxxxxx> <4DE6399C.8070802@xxxxxxxxxx> <20110601134149.GD4266@xxxxxxxxxxxxxxxxx> <4DE64F0C.3050203@xxxxxxxxxx> <20110601152039.GG4266@xxxxxxxxxxxxxxxxx> <4DE66BEB.7040502@xxxxxxxxxx> <BANLkTimbqHPeUdue=_Z31KVdPwcXtbLpeg@xxxxxxxxxxxxxx> <4DE8D50F.1090406@xxxxxxxxxx> <BANLkTinMamg_qesEffGxKu3QkT=zyQ2MRQ@xxxxxxxxxxxxxx> <4DEE26E7.2060201@xxxxxxxxxx> <20110608123527.479e6991.kamezawa.hiroyu@xxxxxxxxxxxxxx> <4DF0801F.9050908@xxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Alpine 2.00 (DEB 1167 2008-08-23)
CC'ing xen-devel and Tim.

This is a comment from a previous email in the thread:

> It most easily reproduced only on xen hvm 32bit guest under heavy vcpus
> contention for real cpus resources (i.e. I had to overcommit cpus and
> run several cpu hog tasks on host to make guest crash on reboot cycle).
> And from last experiments, crash happens only on on hosts that doesn't
> have hap feature or if hap is disabled in hypervisor.

it makes me think that it is a shadow pagetables bug; see details below.
You can find more details on it following this thread on the lkml.




On Thu, 9 Jun 2011, Igor Mammedov wrote:
> On 06/08/2011 05:35 AM, KAMEZAWA Hiroyuki wrote:
> > On Tue, 07 Jun 2011 15:25:59 +0200
> > Igor Mammedov<imammedo@xxxxxxxxxx>  wrote:
> >
> >> Sorry for late reply,
> >>
> >> On 06/03/2011 03:00 PM, Hiroyuki Kamezawa wrote:
> >>> 2011/6/3 Igor Mammedov<imammedo@xxxxxxxxxx>:
> >>>> On 06/02/2011 01:10 AM, Hiroyuki Kamezawa wrote:
> >>>>>> pc = list_entry(list->prev, struct page_cgroup, lru);
> >>>>> Hmm, I disagree your patch is a fix for mainline. At least, a cgroup
> >>>>> before completion of
> >>>>> create() is not populated to userland and you never be able to rmdir()
> >>>>> it because you can't
> >>>>> find it.
> >>>>>
> >>>>>
> >>>>>    >26:   e8 7d 12 30 00          call   0x3012a8
> >>>>>    >2b:*  8b 73 08                mov    0x8(%ebx),%esi<-- trapping
> >>>>> instruction
> >>>>>    >2e:   8b 7c 24 24             mov    0x24(%esp),%edi
> >>>>>    >32:   8b 07                   mov    (%edi),%eax
> >>>>>
> >>>>> Hm, what is the call 0x3012a8 ?
> >>>>>
> >>>>                  pc = list_entry(list->prev, struct page_cgroup, lru);
> >>>>                  if (busy == pc) {
> >>>>                          list_move(&pc->lru, list);
> >>>>                          busy = 0;
> >>>>                          spin_unlock_irqrestore(&zone->lru_lock, flags);
> >>>>                          continue;
> >>>>                  }
> >>>>                  spin_unlock_irqrestore(&zone->lru_lock, flags);<---- is
> >>>>    call 0x3012a8
> >>>>                  ret = mem_cgroup_move_parent(pc, mem, GFP_KERNEL);
> >>>>
> >>>> and  mov 0x8(%ebx),%esi
> >>>> is dereferencing of 'pc' in inlined mem_cgroup_move_parent
> >>>>
> >>> Ah, thank you for input..then panicd at accessing pc->page and "pc"
> >>> was 0xfffffff4.
> >>> it means list->prev was NULL.
> >>>
> >> yes, that's the case.
> >>>> I've looked at vmcore once more and indeed there isn't any parallel task
> >>>> that touches cgroups code path.
> >>>> Will investigate if it is xen to blame for incorrect data in place.
> >>>>
> >>>> Thanks very much for your opinion.
> >>> What curious to me is that the fact "list->prev" is NULL.
> >>> I can see why you doubt the initialization code ....the list pointer never
> >>> contains NULL once it's used....
> >>> it smells like memory corruption or some to me. If you have vmcore,
> >>> what the problematic mem_cgroup_per_zone(node) contains ?
> >> it has all zeros except for last field:
> >>
> >> crash>  rd f3446a00 62
> >> f3446a00:  00000000 00000000 00000000 00000000   ................
> >> f3446a10:  00000000 00000000 00000000 00000000   ................
> >> f3446a20:  00000000 00000000 00000000 00000000   ................
> >> f3446a30:  00000000 00000000 00000000 00000000   ................
> >> f3446a40:  00000000 00000000 00000000 00000000   ................
> >> f3446a50:  00000000 00000000 00000000 00000000   ................
> >> f3446a60:  00000000 00000000 00000000 00000000   ................
> >> f3446a70:  00000000 00000000 f36ef800 f3446a7c   ..........n.|jD.
> >> f3446a80:  f3446a7c f3446a84 f3446a84 f3446a8c   |jD..jD..jD..jD.
> >> f3446a90:  f3446a8c f3446a94 f3446a94 f3446a9c   .jD..jD..jD..jD.
> >> f3446aa0:  f3446a9c 00000000 00000000 00000000   .jD.............
> >> f3446ab0:  00000000 00000000 00000000 00000000   ................
> >> f3446ac0:  00000000 00000000 00000000 00000000   ................
> >> f3446ad0:  00000000 00000000 00000000 00000000   ................
> >> f3446ae0:  00000000 00000000 00000000 00000000   ................
> >> f3446af0:  00000000 f36ef800
> >>
> >> crash>  struct mem_cgroup f36ef800
> >> struct mem_cgroup {
> >> ...
> >> info = {
> >>       nodeinfo = {0xf3446a00}
> >>     },
> >> ...
> >>
> >> It looks like a very targeted corruption of the first zone except of
> >> the last field, while the second zone and the rest are perfectly
> >> normal (i.e. have empty initialized lists).
> >>
> > Hmm, ok, thank you. Then, mem_cgroup_pre_zone[] was initialized once.
> > In this kind of case, I tend to check slab header of memory object f3446a00,
> > or check whether f3446a00 is an alive slab object or not.
> It looks like f3446a00 alive/allocated object
> 
> crash> kmem f3446a00
> CACHE    NAME                 OBJSIZE  ALLOCATED     TOTAL  SLABS  SSIZE
> f7000c80 size-512                 512       2251      2616    327     4k
> SLAB      MEMORY    TOTAL  ALLOCATED  FREE
> f3da6540  f3446000      8          1     7
> FREE / [ALLOCATED]
>    [f3446a00]
> 
>    PAGE    PHYSICAL   MAPPING    INDEX CNT FLAGS
> c1fa58c0  33446000         0        70  1 2800080
> 
> 
> However I have a related crash that can lead to not initialized lists of 
> the first entry
> (i.e. to what we see at f3446a00), debug kernel sometimes will crash at
> alloc_mem_cgroup_per_zone_info:
> 
> XXX: pn: f208dc00, phy: 3208dc00
> XXX: pn: f2e85a00, phy: 32e85a00
> BUG: unable to handle kernel paging request at 9b74e240
> IP: [<c080b95f>] mem_cgroup_create0x+0xef/0x350
> *pdpt = 0000000033542001 *pde = 0000000000000000
> Oops: 0002 [#1] SMP
> ...
> 
> Pid: 1823, comm: libvirtd Tainted: G           ---------------- T
> (2.6.32.700565 #21) HVM domU
> EIP: 0060:[<c080b95f>] EFLAGS: 00210297 CPU: 3
> EIP is at mem_cgroup_create+0xef/0x350
> EAX: 9b74e240 EBX: f2e85a00 ECX: 00000001 EDX: 00000001
> ESI: a88c8840 EDI: a88c8840 EBP: f201deb4 ESP: f201de8c
>   DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
> Process libvirtd (pid: 1823, ti=f201c000 task=f3642ab0 task.ti=f201c000)
> Stack:
>   c09579b2 f2e85a00 32e85a00 f3455800 00000000 f2e85a00 f2c14ac0 c0a5a820
> <0>  fffffff4 f2c14ac0 f201def8 c049d3a7 00000000 00000000 00000000 000001ed
> <0>  f2c14ac8 f5fa4400 f24fe954 f3502000 f2c14e40 f24f5608 f3502010 f2c14ac0
> Call Trace:
>   [<c049d3a7>] cgroup_mkdir+0xf7/0x450
>   [<c05318e3>] vfs_mkdir+0x93/0xf0
>   [<c0533787>] ? lookup_hash+0x27/0x30
>   [<c053390e>] sys_mkdirat+0xde/0x100
>   [<c04b5d4d>] ? call_rcu_sched+0xd/0x10
>   [<c04b5d58>] ? call_rcu+0x8/0x10
>   [<c047ab9f>] ? __put_cred+0x2f/0x50
>   [<c0524ded>] ? sys_faccessat+0x14d/0x180
>   [<c0523fb7>] ? filp_close+0x47/0x70
>   [<c0533950>] sys_mkdir+0x20/0x30
>   [<c0409b5f>] sysenter_do_call+0x12/0x28
> 
> 
> static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
> {
> ...
>          memset(pn, 0, sizeof(*pn));
> 
>          for (zone = 0; zone<  MAX_NR_ZONES; zone++) {
>                  mz =&pn->zoneinfo[zone];
>                  for_each_lru(l)
>                          INIT_LIST_HEAD(&mz->lists[l]);<- crash here
>                  mz->usage_in_excess = 0;
>                  mz->on_tree = false;
>                  mz->mem = mem;
>          }
> ...
> 
> 
> crash>  dis 0xc080b93e 15
> 0xc080b93e<mem_cgroup_create+206>:     movl   $0x0,-0x18(%ebp)
> 0xc080b945<mem_cgroup_create+213>:     mov    %esi,-0x1c(%ebp)
> 0xc080b948<mem_cgroup_create+216>:     imul   $0x7c,-0x18(%ebp),%edi
> 0xc080b94c<mem_cgroup_create+220>:     xor    %ecx,%ecx
> 0xc080b94e<mem_cgroup_create+222>:     xor    %edx,%edx
> 0xc080b950<mem_cgroup_create+224>:     lea    (%edi,%edx,8),%esi
> 0xc080b953<mem_cgroup_create+227>:     add    $0x1,%ecx
> 0xc080b956<mem_cgroup_create+230>:     lea    (%ebx,%esi,1),%eax
> 0xc080b959<mem_cgroup_create+233>:     add    $0x1,%edx
> 0xc080b95c<mem_cgroup_create+236>:     cmp    $0x5,%ecx
> 0xc080b95f<mem_cgroup_create+239>:     mov    %eax,(%ebx,%esi,1)
> 0xc080b962<mem_cgroup_create+242>:     mov    %eax,0x4(%eax)
> 0xc080b965<mem_cgroup_create+245>:     jne    0xc080b950
> 0xc080b967<mem_cgroup_create+247>:     mov    -0x14(%ebp),%eax
> 0xc080b96a<mem_cgroup_create+250>:     movl   $0x0,0x6c(%eax)
> 
> EDI on the first iteration should be 0 however it is a88c8840 according to 
> Oops
> dump and looking at -0x18(%ebp) in core shows 0 as it should be:
> 
> crash>  x/xw 0xf201deb4-0x18
> 0xf201de9c:     0x00000000
> 
> so it looks like EDI is incorrectly restored by Xen or at the moment when 
> 0xc080b948
> was executed -0x18(%ebp) had that weird value.
> 
> It is possible that invalid EDI value and following
> 
> 0xc080b950<mem_cgroup_create+224>:     lea    (%edi,%edx,8),%esi
> 
> <https://bugzilla.redhat.com/show_bug.cgi?id=700565#c36>lead to some 
> accessible page and writes
> 
> 0xc080b95f<mem_cgroup_create+239>:     mov    %eax,(%ebx,%esi,1)
> 0xc080b962<mem_cgroup_create+242>:     mov    %eax,0x4(%eax)
> 
> silently go to that page. Than after init lists loop it uses correct pn 
> offset from
> -0x14(%ebp) and initialises the rest fields of structure on the correct page.
> 
>                  mz->usage_in_excess = 0;
>                  mz->on_tree = false;
>                  mz->mem = mem;
> 
> 0xc080b967<mem_cgroup_create+247>:     mov    -0x14(%ebp),%eax<-
> 0xc080b96a<mem_cgroup_create+250>:     movl   $0x0,0x6c(%eax)
> 0xc080b971<mem_cgroup_create+257>:     movl   $0x0,0x70(%eax)
> 0xc080b978<mem_cgroup_create+264>:     movb   $0x0,0x74(%eax)
> 0xc080b97c<mem_cgroup_create+268>:     mov    -0x1c(%ebp),%edx
> 0xc080b97f<mem_cgroup_create+271>:     mov    %edx,0x78(%eax)
> 0xc080b982<mem_cgroup_create+274>:     add    $0x7c,%eax
> 0xc080b985<mem_cgroup_create+277>:     addl   $0x1,-0x18(%ebp)
> 0xc080b989<mem_cgroup_create+281>:     cmpl   $0x4,-0x18(%ebp)
> 0xc080b98d<mem_cgroup_create+285>:     mov    %eax,-0x14(%ebp)
> 0xc080b990<mem_cgroup_create+288>:     jne    0xc080b948
> 
> which could lead to the 0-ed list entries of the first zone
> and the originally reported Oops in mem_cgroup_force_empty.
> Afterwards it looks like:
> 
> 0xc080b985<mem_cgroup_create+277>:     addl   $0x1,-0x18(%ebp)
> 
> -0x18(%ebp) is read correctly and the rest of 3 mz entries are initialized as
> expected.
> 
> So question is why and how
> 0xc080b948<mem_cgroup_create+216>:     imul   $0x7c,-0x18(%ebp),%edi
> may be screwed up
> 
> PS:
> However, memory search for the went astray writes of the first entry
> i.e. sequesnce f3446a00 f3446a00 in a couple of vmcores didn't give
> any positive results.
> 
> 
> > Thanks,
> > -Kame
> >> PS:
> >> It most easily reproduced only on xen hvm 32bit guest under heavy
> >> vcpus contention for real cpus resources (i.e. I had to overcommit
> >> cpus and run several cpu hog tasks on host to make guest crash on
> >> reboot cycle).
> >> And from last experiments, crash happens only on on hosts that
> >> doesn't have hap feature or if hap is disabled in hypervisor.
> >>
> >>> Thanks,
> >>> -Kame
> >>
> 

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel

<Prev in Thread] Current Thread [Next in Thread>