Re: kernel panic in skb_copy_bits

[Eric Dumazet <eric.dumazet@gmail.com>]

On Fri, 2013-06-28 at 12:17 +0800, Joe Jin wrote:
> Find a similar issue  http://www.gossamer-threads.com/lists/xen/devel/265611
> So copied to Xen developer as well.
> 
> On 06/27/13 13:31, Eric Dumazet wrote:
> > On Thu, 2013-06-27 at 10:58 +0800, Joe Jin wrote:
> >> Hi,
> >>
> >> When we do fail over test with iscsi + multipath by reset the switches
> >> on OVM(2.6.39) we hit the panic:
> >>
> >> BUG: unable to handle kernel paging request at ffff88006d9e8d48
> >> IP: [<ffffffff812605bb>] memcpy+0xb/0x120
> >> PGD 1798067 PUD 1fd2067 PMD 213f067 PTE 0
> >> Oops: 0000 [#1] SMP 
> >> CPU 7 
> >> Modules linked in: dm_nfs tun nfs fscache auth_rpcgss nfs_acl xen_blkback xen_netback xen_gntdev xen_evtchn lockd sunrpc bridge stp llc bonding be2iscsi iscsi_boot_sysfs ib_iser rdma_cm ib_cm iw_cm ib_sa ib_mad ib_core ib_addr iscsi_tcp bnx2i cnic uio ipv6 cxgb3i libcxgbi cxgb3 mdio dm_round_robin dm_multipath libiscsi_tcp libiscsi scsi_transport_iscsi xenfs xen_privcmd video sbs sbshc acpi_memhotplug acpi_ipmi ipmi_msghandler parport_pc lp parport ixgbe dca sr_mod cdrom bnx2 radeon ttm drm_kms_helper drm snd_seq_dummy i2c_algo_bit i2c_core snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss serio_raw snd_pcm snd_timer snd soundcore snd_page_alloc iTCO_wdt pcspkr iTCO_vendor_support pata_acpi dcdbas i5k_amb ata_generic hwmon floppy ghes i5000_edac edac_core
  hed dm_snapshot dm_zero dm_mirror dm_region_hash dm_log dm_mod usb_storage lpfc scsi_transport_fc scsi_tgt ata_piix sg shpchp mptsas mptscsih mptbase scsi_transport_sas sd_mod crc_t10dif ext!
>  3!
> >   j!
> >>  bd mbcache
> >>
> >>
> >> Pid: 0, comm: swapper Tainted: G        W   2.6.39-300.32.1.el5uek #1 Dell Inc. PowerEdge 2950/0DP246
> >> RIP: e030:[<ffffffff812605bb>]  [<ffffffff812605bb>] memcpy+0xb/0x120
> >> RSP: e02b:ffff8801003c3d58  EFLAGS: 00010246
> >> RAX: ffff880076b9e280 RBX: ffff8800714d2c00 RCX: 0000000000000057
> >> RDX: 0000000000000000 RSI: ffff88006d9e8d48 RDI: ffff880076b9e280
> >> RBP: ffff8801003c3dc0 R08: 00000000000bf723 R09: 0000000000000000
> >> R10: 0000000000000000 R11: 000000000000000a R12: 0000000000000034
> >> R13: 0000000000000034 R14: 00000000000002b8 R15: 00000000000005a8
> >> FS:  00007fc1e852a6e0(0000) GS:ffff8801003c0000(0000) knlGS:0000000000000000
> >> CS:  e033 DS: 002b ES: 002b CR0: 000000008005003b
> >> CR2: ffff88006d9e8d48 CR3: 000000006370b000 CR4: 0000000000002660
> >> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> >> Process swapper (pid: 0, threadinfo ffff880077ac0000, task ffff880077abe240)
> >> Stack:
> >>  ffffffff8142db21 0000000000000000 ffff880076b9e280 ffff8800637097f0
> >>  000002ec00000000 00000000000002b8 ffff880077ac0000 0000000000000000
> >>  ffff8800637097f0 ffff880066c9a7c0 00000000fffffdb4 000000000000024c
> >> Call Trace:
> >>  <IRQ> 
> >>  [<ffffffff8142db21>] ? skb_copy_bits+0x1c1/0x2e0
> >>  [<ffffffff8142f173>] skb_copy+0xf3/0x120
> >>  [<ffffffff81447fbc>] neigh_timer_handler+0x1ac/0x350
> >>  [<ffffffff810573fe>] ? account_idle_ticks+0xe/0x10
> >>  [<ffffffff81447e10>] ? neigh_alloc+0x180/0x180
> >>  [<ffffffff8107dbaa>] call_timer_fn+0x4a/0x110
> >>  [<ffffffff81447e10>] ? neigh_alloc+0x180/0x180
> >>  [<ffffffff8107f82a>] run_timer_softirq+0x13a/0x220
> >>  [<ffffffff81075c39>] __do_softirq+0xb9/0x1d0
> >>  [<ffffffff810d9678>] ? handle_percpu_irq+0x48/0x70
> >>  [<ffffffff81511d3c>] call_softirq+0x1c/0x30
> >>  [<ffffffff810172e5>] do_softirq+0x65/0xa0
> >>  [<ffffffff8107656b>] irq_exit+0xab/0xc0
> >>  [<ffffffff812f97d5>] xen_evtchn_do_upcall+0x35/0x50
> >>  [<ffffffff81511d8e>] xen_do_hypervisor_callback+0x1e/0x30
> >>  <EOI> 
> >>  [<ffffffff810013aa>] ? xen_hypercall_sched_op+0xa/0x20
> >>  [<ffffffff810013aa>] ? xen_hypercall_sched_op+0xa/0x20
> >>  [<ffffffff8100a0b0>] ? xen_safe_halt+0x10/0x20
> >>  [<ffffffff8101dfeb>] ? default_idle+0x5b/0x170
> >>  [<ffffffff81014ac6>] ? cpu_idle+0xc6/0xf0
> >>  [<ffffffff8100a8c9>] ? xen_irq_enable_direct_reloc+0x4/0x4
> >>  [<ffffffff814f7bbe>] ? cpu_bringup_and_idle+0xe/0x10
> >> Code: 01 c6 43 4c 04 19 c0 4c 8b 65 f0 4c 8b 6d f8 83 e0 fc 83 c0 08 88 43 4d 48 8b 5d e8 c9 c3 90 90 48 89 f8 89 d1 c1 e9 03 83 e2 07 <f3> 48 a5 89 d1 f3 a4 c3 20 48 83 ea 20 4c 8b 06 4c 8b 4e 08 4c 
> >> RIP  [<ffffffff812605bb>] memcpy+0xb/0x120
> >>  RSP <ffff8801003c3d58>
> >> CR2: ffff88006d9e8d48
> >>
> >> Reviewed vmcore I found the skb->users is 1 at the moment, checked network neighbour 
> >> history I found skb_get() be replaced by skb_copy by commit 7e36763b2c:
> >>
> >> commit 7e36763b2c204d59de4e88087f84a2c0c8421f25                               
> >> Author: Frank Blaschka <frank.blaschka@de.ibm.com>                            
> >> Date:   Mon Mar 3 12:16:04 2008 -0800
> >>
> >>     [NET]: Fix race in generic address resolution.                            
> >>         
> >>     neigh_update sends skb from neigh->arp_queue while neigh_timer_handler    
> >>     has increased skbs refcount and calls solicit with the                    
> >>     skb. neigh_timer_handler should not increase skbs refcount but make a     
> >>     copy of the skb and do solicit with the copy.                             
> >>     
> >>     Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>                 
> >>     Signed-off-by: David S. Miller <davem@davemloft.net>                      
> >>
> >> So can you please give some details of the race? per vmcore seems like the skb data
> >> be freed, I suspected skb_get() lost at somewhere?
> >> I reverted above commit the panic not occurred during our testing.
> >>
> >> Any input will appreciate!
> > 
> > Well, fact is that your crash is happening in skb_copy().
> > 
> > Frank patch is OK. I suspect using skb_clone() would work too,
> > so if these skb were fclone ready, chance of an GFP_ATOMIC allocation
> > error would be smaller.
> > 
> > So something is providing a wrong skb at the very beginning.
> > 
> > You could try to do a early skb_copy to catch the bug and see in the
> > stack trace what produced this buggy skb.
> > 
> > diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> > index 5c56b21..a7a51fd 100644
> > --- a/net/core/neighbour.c
> > +++ b/net/core/neighbour.c
> > @@ -1010,6 +1010,7 @@ int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)
> >  				NEIGH_CACHE_STAT_INC(neigh->tbl, unres_discards);
> >  			}
> >  			skb_dst_force(skb);
> > +			kfree_skb(skb_copy(skb, GFP_ATOMIC));
> >  			__skb_queue_tail(&neigh->arp_queue, skb);
> >  			neigh->arp_queue_len_bytes += skb->truesize;
> >  		}
> > 
> > 
> 
> BUG: unable to handle kernel paging request at ffff8800488db8dc
> IP: [<ffffffff812605bb>] memcpy+0xb/0x120
> PGD 1796067 PUD 20e5067 PMD 212a067 PTE 0
> Oops: 0000 [#1] SMP 
> CPU 13 
> Modules linked in: ocfs2 jbd2 xen_blkback xen_netback xen_gntdev xen_evtchn netconsole i2c_dev i2c_core ocfs2_dlmfs ocfs2_stack_o2cb ocfs2_dlm ocfs2_nodemanager ocfs2_stackglue configfs lockd sunrpc dm_round_robin dm_multipath bridge stp llc bonding be2iscsi iscsi_boot_sysfs iscsi_tcp bnx2i cnic uio ipv6 cxgb3i libcxgbi cxgb3 mdio libiscsi_tcp libiscsi scsi_transport_iscsi xenfs xen_privcmd video sbs sbshc hed acpi_memhotplug acpi_ipmi ipmi_msghandler parport_pc lp parport serio_raw ixgbe hpilo tg3 hpwdt dca snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss snd_pcm snd_timer snd iTCO_wdt iTCO_vendor_support soundcore snd_page_alloc pcspkr pata_acpi ata_generic dm_snapshot dm_zero dm_mirror dm_region_hash dm_log dm_mod usb_storage ata_piix sg sh
 pchp hpsa cciss sd_mod crc_t10dif ext3 jbd mbcache
> 
> Pid: 0, comm: swapper Not tainted 2.6.39-300.32.1.el5uek.bug16929255v5 #1 HP ProLiant DL360p Gen8
> RIP: e030:[<ffffffff812605bb>]  [<ffffffff812605bb>] memcpy+0xb/0x120
> RSP: e02b:ffff88005a9a3b68  EFLAGS: 00010202
> RAX: ffff8800200f0280 RBX: 0000000000000724 RCX: 00000000000000e4
> RDX: 0000000000000004 RSI: ffff8800488db8dc RDI: ffff8800200f0280
> RBP: ffff88005a9a3bd0 R08: 0000000000000004 R09: ffff880052824980
> R10: 0000000000000000 R11: 0000000000015048 R12: 0000000000000034
> R13: 0000000000000034 R14: 00000000000022f4 R15: ffff880021208ab0
> FS:  00007fe8737c96e0(0000) GS:ffff88005a9a0000(0000) knlGS:0000000000000000
> CS:  e033 DS: 002b ES: 002b CR0: 000000008005003b
> CR2: ffff8800488db8dc CR3: 000000004fb38000 CR4: 0000000000002660
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Process swapper (pid: 0, threadinfo ffff880054d36000, task ffff880054d343c0)
> Stack:
>  ffffffff8142dac7 0000000000000000 00000000ffffffff ffff8800200f0280
>  0000075800000000 0000000000000724 ffff880054d36000 0000000000000000
>  00000000fffffdb4 ffff880052824980 ffff880021208ab0 000000000000024c
> Call Trace:
>  <IRQ> 
>  [<ffffffff8142dac7>] ? skb_copy_bits+0x167/0x290
>  [<ffffffff8142f0b5>] skb_copy+0x85/0xb0
>  [<ffffffff8144864d>] __neigh_event_send+0x18d/0x200
>  [<ffffffff81449a42>] neigh_resolve_output+0x162/0x1b0
>  [<ffffffff81477046>] ip_finish_output+0x146/0x320
>  [<ffffffff814754a5>] ip_output+0x85/0xd0
>  [<ffffffff814758d9>] ip_local_out+0x29/0x30
>  [<ffffffff814761e0>] ip_queue_xmit+0x1c0/0x3d0
>  [<ffffffff8148d3ef>] tcp_transmit_skb+0x40f/0x520
>  [<ffffffff8148e5ff>] tcp_retransmit_skb+0x16f/0x2e0
>  [<ffffffff814908c0>] ? tcp_retransmit_timer+0x4a0/0x4a0
>  [<ffffffff814905ad>] tcp_retransmit_timer+0x18d/0x4a0
>  [<ffffffff814908c0>] ? tcp_retransmit_timer+0x4a0/0x4a0
>  [<ffffffff81490994>] tcp_write_timer+0xd4/0x100
>  [<ffffffff8107dbaa>] call_timer_fn+0x4a/0x110
>  [<ffffffff814908c0>] ? tcp_retransmit_timer+0x4a0/0x4a0
>  [<ffffffff8107f82a>] run_timer_softirq+0x13a/0x220
>  [<ffffffff81075c39>] __do_softirq+0xb9/0x1d0
>  [<ffffffff810d9678>] ? handle_percpu_irq+0x48/0x70
>  [<ffffffff81511b7c>] call_softirq+0x1c/0x30
>  [<ffffffff810172e5>] do_softirq+0x65/0xa0
>  [<ffffffff8107656b>] irq_exit+0xab/0xc0
>  [<ffffffff812f97d5>] xen_evtchn_do_upcall+0x35/0x50
>  [<ffffffff81511bce>] xen_do_hypervisor_callback+0x1e/0x30
>  <EOI> 
>  [<ffffffff810013aa>] ? xen_hypercall_sched_op+0xa/0x20
>  [<ffffffff810013aa>] ? xen_hypercall_sched_op+0xa/0x20
>  [<ffffffff8100a0d0>] ? xen_safe_halt+0x10/0x20
>  [<ffffffff8101dfeb>] ? default_idle+0x5b/0x170
>  [<ffffffff81014ac6>] ? cpu_idle+0xc6/0xf0
>  [<ffffffff8100a8e9>] ? xen_irq_enable_direct_reloc+0x4/0x4
>  [<ffffffff814f7a2e>] ? cpu_bringup_and_idle+0xe/0x10
> Code: 01 c6 43 4c 04 19 c0 4c 8b 65 f0 4c 8b 6d f8 83 e0 fc 83 c0 08 88 43 4d 48 8b 5d e8 c9 c3 90 90 48 89 f8 89 d1 c1 e9 03 83 e2 07 <f3> 48 a5 89 d1 f3 a4 c3 20 48 83 ea 20 4c 8b 06 4c 8b 4e 08 4c 
> RIP  [<ffffffff812605bb>] memcpy+0xb/0x120
> 
> 
> Per vmcore, the socket info as below:
> ------------------------------------------------------------------------------
> <struct tcp_sock 0xffff88004d344e00>            TCP
> tcp   10.1.1.11:42147            10.1.1.21:3260              FIN_WAIT1
>         windows: rcv=122124, snd=65535  advmss=8948 rcv_ws=1 snd_ws=0
>         nonagle=1 sack_ok=0 tstamp_ok=1
>         rmem_alloc=0, wmem_alloc=10229
>         rx_queue=0, tx_queue=149765
>         rcvbuf=262142, sndbuf=262142
>         rcv_tstamp=51.4 s, lsndtime=0.0 s  ago
>     -- Retransmissions --
>        retransmits=7, ca_state=TCP_CA_Disorder
> ------------------------------------------------------------------------------
> 
> When sock status move to FIN_WAIT1, will it cleanup all skb or no?

I get crashes as well using UDP application. Its not related to TCP.

There is some corruption going on in neighbour code.

[  942.319645] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
[  942.327510] IP: [<ffffffff814e4558>] __neigh_event_send+0x1a8/0x240
[  942.333799] PGD c5a125067 PUD c603e1067 PMD 0
[  942.338292] Oops: 0002 [#1] SMP
[  942.341819] gsmi: Log Shutdown Reason 0x03
[  942.364995] CPU: 8 PID: 13760 Comm: netperf Tainted: G        W    3.10.0-smp-DEV #155
[  942.380212] task: ffff88065b54b000 ti: ffff8806498fc000 task.ti: ffff8806498fc000
[  942.387689] RIP: 0010:[<ffffffff814e4558>]  [<ffffffff814e4558>] __neigh_event_send+0x1a8/0x240
[  942.396402] RSP: 0018:ffff8806498fd9d8  EFLAGS: 00010206
[  942.401709] RAX: 0000000000000000 RBX: ffff88065a8f9000 RCX: ffff88065fdf61c0
[  942.408837] RDX: 0000000000000000 RSI: ffff880c5d5b3080 RDI: ffff880c5b9c0ac0
[  942.415966] RBP: ffff8806498fd9f8 R08: ffff88064cb00000 R09: ffff8806498fda70
[  942.423095] R10: ffff880c5ffbead0 R11: ffffffff815137d0 R12: ffff88065a8f9030
[  942.430232] R13: ffff880c5d5b3080 R14: 0000000000000000 R15: ffff88065b4af940
[  942.437362] FS:  00007fd613190700(0000) GS:ffff880c7fc40000(0000) knlGS:0000000000000000
[  942.445452] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  942.451193] CR2: 0000000000000008 CR3: 0000000c59b60000 CR4: 00000000000007e0
[  942.458324] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  942.465460] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Jun 27 05:49:12 [  942.472597] Stack:
[  942.475997]  ffff880c5d5b3080 ffff88065a8f9000 ffff880c59ac43c0 0000000000000088
[  942.483473]  ffff8806498fda48 ffffffff814e50db ffff880c5d5b3080 ffffffff81514c60
[  942.490947]  0000000000000088 ffff88064cb00000 ffff880c5d5b3080 ffff880c59ac43c0
[  942.498415] Call Trace:
[  942.500873]  [<ffffffff814e50db>] neigh_resolve_output+0x14b/0x1f0
lpq84 kernel: [ [  942.507056]  [<ffffffff81514c60>] ? __ip_append_data.isra.39+0x9e0/0x9e0
[  942.515138]  [<ffffffff81514ddf>] ip_finish_output+0x17f/0x380
[  942.520972]  [<ffffffff81515bb3>] ip_output+0x53/0x90
 942.341819] gsm[  942.526030]  [<ffffffff815167d6>] ? ip_make_skb+0xf6/0x120
[  942.532897]  [<ffffffff81515379>] ip_local_out+0x29/0x30
i: Log Shutdown [  942.538215]  [<ffffffff81516649>] ip_send_skb+0x19/0x50
Reason 0x03
[  942.544825]  [<ffffffff8153a65e>] udp_send_skb+0x2ce/0x3a0
[  942.551439]  [<ffffffff815137d0>] ? ip_setup_cork+0x110/0x110