Subject: Re: [vserver] Again: [vserver] Linux vServer: general protection fault with apache2 and kernel 2.6.38.6
From: Herbert Poetzl <herbert@13thfloor.at>
Date: Sat, 6 Aug 2011 20:32:02 +0200

On Sat, Aug 06, 2011 at 03:01:27PM +0200, Urban Loesch wrote:


> Am 06.08.2011 14:38, schrieb Herbert Poetzl:
>> On Sat, Aug 06, 2011 at 02:13:37PM +0200, Urban Loesch wrote:

>>> Hi Herbert,
>>>> I just tried to pinpoint the location based on my
>>>> 2.6.38.8-vs2.3.0.37-rc17 kernel and I suspect that
>>>> task_rq(p) is causing this (for certain p), but
>>>> I was wondering why your task_rq_lock() is 0xa0
>>>> bytes in size, where mine is just 0x65 bytes ...
>>>> especially as the task_rq_lock function is quite
>>>> compact ...
>>>> could you upload the output of the folling commands
>>>> for me (executed in the build directory of your
>>>> kernel or with the vmlinux object file)
>>>> # objdump -t vmlinux | grep task_rq_lock
>>> gives me only on line:
>> that's fine, nothing more was expected :)

>>> /usr/src/linux-2.6.38.8 # objdump -t vmlinux | grep task_rq_lock
>>> ffffffff8104ec60 l     F .text	000000000000009c task_rq_lock
>>>> # objdump -d vmlinux --start-address=0x`objdump -t vmlinux | sed -n
>>>> '/task_rq_lock/ {s/ .*//; p}'` | sed '/task>:/ Q'
>>> more lines :-)
>>> You can download it at http://www.enas.net/objdump.txt
>> I copied the interesting part here:

>> ffffffff8104ec60<task_rq_lock>:
>> ffffffff8104ec60:	55                   	push   %rbp
>> ffffffff8104ec61:	48 89 e5             	mov    %rsp,%rbp
>> ffffffff8104ec64:	48 83 ec 20          	sub    $0x20,%rsp
>> ffffffff8104ec68:	48 89 1c 24          	mov    %rbx,(%rsp)
>> ffffffff8104ec6c:	4c 89 64 24 08       	mov    %r12,0x8(%rsp)
>> ffffffff8104ec71:	4c 89 6c 24 10       	mov    %r13,0x10(%rsp)
>> ffffffff8104ec76:	4c 89 74 24 18       	mov    %r14,0x18(%rsp)
>> ffffffff8104ec7b:	e8 40 d0 fb ff       	callq  
>> ffffffff8100bcc0<mcount>

>> this suggests that you have FTRACE enabled in your
>> kernel and probably a bunch of related TRACERS

>> ffffffff8104ec80:	48 c7 c3 40 3c 01 00 	mov    $0x13c40,%rbx
>> ffffffff8104ec87:	49 89 fc             	mov    %rdi,%r12
>> ffffffff8104ec8a:	49 89 f5             	mov    %rsi,%r13
>> ffffffff8104ec8d:	ff 14 25 00 34 a1 81 	callq  *0xffffffff81a13400
>> ffffffff8104ec94:	48 89 c2             	mov    %rax,%rdx
>> ffffffff8104ec97:	ff 14 25 10 34 a1 81 	callq  *0xffffffff81a13410
>> ffffffff8104ec9e:	49 89 55 00          	mov    %rdx,0x0(%r13)
>> ffffffff8104eca2:	49 8b 44 24 08       	mov    0x8(%r12),%rax
>> ffffffff8104eca7:	49 89 de             	mov    %rbx,%r14
>> ffffffff8104ecaa:	8b 40 18             	mov    0x18(%rax),%eax
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

>> this is where your problem happens, and together with
>> the information from the original post (which you
>> removed) this looks like task_rq looking for a task at
>> 0x9066669066666605 which is rather unlikely to be a
>> valid address, so to me this looks like some kind of
>> memory corruption, maybe caused by a completely
>> different subsystem ...

>> ffffffff8104ecad:	4c 03 34 c5 00 d4 ab 	add    
>> -0x7e542c00(,%rax,8),%r14
>> ffffffff8104ecb4:	81
>> ffffffff8104ecb5:	4c 89 f7             	mov    %r14,%rdi
>> ffffffff8104ecb8:	e8 43 14 54 00       	callq  
>> ffffffff81590100<_raw_spin_lock>
>> ffffffff8104ecbd:	49 8b 44 24 08       	mov    0x8(%r12),%rax
>> ffffffff8104ecc2:	8b 40 18             	mov    0x18(%rax),%eax
>> ffffffff8104ecc5:	48 8b 14 c5 00 d4 ab 	mov    
>> -0x7e542c00(,%rax,8),%rdx
>> ffffffff8104eccc:	81
>> ffffffff8104eccd:	48 8d 04 13          	lea    (%rbx,%rdx,1),%rax
>> ffffffff8104ecd1:	49 39 c6             	cmp    %rax,%r14
>> ffffffff8104ecd4:	75 18                	jne    
>> ffffffff8104ecee<task_rq_lock+0x8e>
>> ffffffff8104ecd6:	4c 89 f0             	mov    %r14,%rax
>> ffffffff8104ecd9:	48 8b 1c 24          	mov    (%rsp),%rbx
>> ffffffff8104ecdd:	4c 8b 64 24 08       	mov    0x8(%rsp),%r12
>> ffffffff8104ece2:	4c 8b 6c 24 10       	mov    0x10(%rsp),%r13
>> ffffffff8104ece7:	4c 8b 74 24 18       	mov    0x18(%rsp),%r14
>> ffffffff8104ecec:	c9                   	leaveq
>> ffffffff8104eced:	c3                   	retq
>> ffffffff8104ecee:	49 8b 75 00          	mov    0x0(%r13),%rsi
>> ffffffff8104ecf2:	4c 89 f7             	mov    %r14,%rdi
>> ffffffff8104ecf5:	e8 86 14 54 00       	callq  
>> ffffffff81590180<_raw_spin_unlock_irqrestore>
>> ffffffff8104ecfa:	eb 91                	jmp    
>> ffffffff8104ec8d<task_rq_lock+0x2d>
>> ffffffff8104ecfc:	0f 1f 40 00          	nopl   0x0(%rax)

>> but that's just a wild guess and some hand waving, to
>> get better information and more debug info we would
>> first need to find a way to trigger this issue within
>> a short amount of time, let's say a few minutes up to
>> an hour or so ...

> I have no idea how can I do this.

setup a test system, where you can hit one of your guests
(or several of them at once) with artificial stress tests
(like a page impression performance test or so) and
monitor the kernel output (best via serial console)

compile the kernel with DEBUG_INFO enabled so that we
can more precise pinpointing in case of a kernel trace

>> btw, does it happen on more than one system or is it
>> always the same system?

> This happend on two of my servers with heavy apache load.
> DELL PE R610 and PE R410. Both with 32GB of ram.

> The first time was in June on my R410 with kernel 2.6.38.6-vs2.3.0.37-rc15
> It gets me the following error in syslog:

> BUG: unable to handle kernel paging request at 00000000801f0f1d
> [2472685.774427] IP: [<ffffffff8103695a>] task_rq_lock+0x4a/0xa0
> [2472685.774505] PGD 3164b1067 PUD 0
> [2472685.774574] Oops: 0000 [#1] SMP
> [2472685.774647] last sysfs file: /sys/module/drbd/parameters/cn_idx
> [2472685.774716] CPU 9
> [2472685.774723] Modules linked in: dca netconsole configfs drbd 
> lru_cache sch_hfsc ip6_queue act_police cls_flow cls_fw cls_u32 sch_htb 
> sch_ingress sch_sfq xt_realm iptable_raw ip6t_LOG xt_connlimit ipt_ULOG 
> ipt_REJECT ip6table_raw ipt_REDIRECT ipt_NETMAP ipt_MASQUERADE ipt_ECN 
> ipt_ecn ipt_CLUSTERIP ipt_ah ipt_addrtype nf_nat_tftp nf_nat_snmp_basic 
> nf_nat_sip xt_comment nf_nat_pptp ip6t_REJECT nf_nat_proto_gre 
> nf_nat_irc nf_nat_h323 nf_nat_ftp nf_nat_amanda xt_recent 
> ip6table_mangle nf_conntrack_ipv6 nf_conntrack_tftp nf_conntrack_sip 
> nf_conntrack_sane nf_conntrack_proto_udplite nf_conntrack_proto_sctp 
> nf_conntrack_pptp nf_conntrack_proto_gre nf_conntrack_netlink 
> nf_conntrack_netbios_ns nf_conntrack_irc nf_conntrack_h323 
> nf_conntrack_ftp ts_kmp nf_conntrack_amanda xt_TPROXY nf_tproxy_core 
> nf_defrag_ipv6 xt_time xt_TCPMSS xt_tcpmss xt_sctp xt_NFLOG 
> nfnetlink_log xt_policy xt_pkttype xt_physdev xt_owner xt_NFQUEUE 
> xt_multiport ipt_LOG xt_mark xt_mac xt_limit iptable_nat xt_length 
> xt_iprange nf_nat xt_helper nf_conntrack_ipv4 xt_hashlimit 
> nf_defrag_ipv4 xt_DSCP xt_dscp iptable_mangle xt_dccp xt_connmark 
> xt_CLASSIFY xt_tcpudp xt_state xt_conntrack nf_conntrack nfnetlink 
> iptable_filter ip_tables ip6table_filter ip6_tables x_tables 
> ipmi_devintf ipmi_si ipmi_msghandler mptctl psmouse processor joydev 
> serio_raw tpm_tis tpm i7core_edac pcspkr tpm_bios edac_core dcdbas 
> power_meter button mptsas mptscsih mptbase usbhid bnx2 
> scsi_transport_sas hid e1000e [last unloaded: igb]
> [2472685.776398]
> [2472685.776459] Pid: 19778, comm: apache2 Not tainted 
> 2.6.38.6-vs2.3.0.37-rc15-rol-em64t #7 Dell Inc. PowerEdge R410/0N051F
> [2472685.776608] RIP: 0010:[<ffffffff8103695a>]  [<ffffffff8103695a>] 
> task_rq_lock+0x4a/0xa0
> [2472685.776743] RSP: 0018:ffff880121b75dc8  EFLAGS: 00010082
> [2472685.776811] RAX: 00000000801f0f05 RBX: 0000000000011d00 RCX: 
> 0000000000000040
> [2472685.776936] RDX: 0000000000000282 RSI: ffff880121b75e20 RDI: 
> 00007f4cfa5fd9a0
> [2472685.777057] RBP: ffff880121b75de8 R08: dead000000200200 R09: 
> dead000000100100
> [2472685.777178] R10: dead000000200200 R11: dead000000100100 R12: 
> 00007f4cfa5fd9a0
> [2472685.777299] R13: ffff880121b75e20 R14: 0000000000011d00 R15: 
> 0000000000000000
> [2472685.777420] FS:  00007f4cfb0a2730(0000) GS:ffff8800bf480000(0000) 
> knlGS:0000000000000000
> [2472685.777542] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [2472685.777608] CR2: 00000000801f0f1d CR3: 00000002884d7000 CR4: 
> 00000000000006e0
> [2472685.777728] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 
> 0000000000000000
> [2472685.777848] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 
> 0000000000000400
> [2472685.777968] Process apache2 (pid: 19778, threadinfo 
> ffff880121b74000, task ffff8801167114d0)
> [2472685.778091] Stack:
> [2472685.778150]  00007f4cfa5fd9a0 ffff88044db61eb8 000000000000000f 
> 0000000000000000
> [2472685.778280]  ffff880121b75e58 ffffffff81040bd6 ffff880121b75e48 
> ffffffff81269f47
> [2472685.778410]  0000000000000000 ffff88081eaafe30 ffff880121b75e28 
> 0000000000000282
> [2472685.778540] Call Trace:
> [2472685.778604]  [<ffffffff81040bd6>] try_to_wake_up+0x36/0x310
> [2472685.778671]  [<ffffffff81269f47>] ? idr_remove+0x187/0x1f0
> [2472685.778739]  [<ffffffff81040f05>] wake_up_process+0x15/0x20
> [2472685.778806]  [<ffffffff81231580>] freeary+0x1e0/0x260
> [2472685.778872]  [<ffffffff81232631>] T.616+0x71/0xf0
> [2472685.778939]  [<ffffffff8113376b>] ? fput+0x1cb/0x280
> [2472685.779005]  [<ffffffff81232719>] sys_semctl+0x69/0xa0
> [2472685.779074]  [<ffffffff81002882>] system_call_fastpath+0x16/0x1b
> [2472685.779142] Code: 00 48 c7 c3 00 1d 01 00 49 89 fc 49 89 f5 9c 58 
> 0f 1f 44 00 00 48 89 c2 fa 66 0f 1f 44 00 00 49 89 55 00 49 8b 44 24 08 
> 49 89 de <8b> 40 18 4c 03 34 c5 e0 b2 70 81 4c 89 f7 e8 73 93 4a 00 49 8b
> [2472685.779515] RIP  [<ffffffff8103695a>] task_rq_lock+0x4a/0xa0
> [2472685.779584]  RSP <ffff880121b75dc8>
> [2472685.779647] CR2: 00000000801f0f1d
> [2472685.780031] ---[ end trace 63c260cc5b2dc0a5 ]---

> On this server are running 4 vServers (all with debian lenny and apache 
> installed).
> On my PER610 is running only one vServer with debian etch (apache, 
> php5-fcgi, mysql 5.0).

interestingly both kernel traces include sys_semctl, so
it might be related to the code handling the semaphores
maybe just try to bang on that a little (from inside the
guest) to see if something triggers ...

best,
Herbert

> thanks,
> Urban

>> best,
>> Herbert

>>> thanks,
>>> Urban