[Xen-devel] netback Oops then xenwatch stuck in D state

["Christopher S. Aker" <caker@xxxxxxxxxxxx>]

We've been hitting the following issue on a variety of hosts and recent 
Xen/dom0 version combinations.  Here's an excerpt from our latest:
Xen: 4.1.4 (xenbits @ 23432)
Dom0: 3.7.1-x86_64

BUG: unable to handle kernel NULL pointer dereference at 000000000000001c
IP: [<ffffffff8141a301>] evtchn_from_irq+0x11/0x40
PGD 0
Oops: 0000 [#1] SMP
Modules linked in: ebt_comment ebt_arp ebt_set ebt_limit ebt_ip6 ebt_ip 
ip_set_hash_net ip_set ebtable_nat xen_gntdev bonding ebtable_filter igb
CPU 0
Pid: 1636, comm: netback/0 Not tainted 3.7.1-x86_64 #1 Supermicro 
X9DRi-LN4+/X9DR3-LN4+/X9DRi-LN4+/X9DR3-LN4+
RIP: e030:[<ffffffff8141a301>]  [<ffffffff8141a301>] 
evtchn_from_irq+0x11/0x40
RSP: e02b:ffff88004334fc98  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff880004964700 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 00000000000001dc RDI: 000000000000001c
RBP: ffff88004334fc98 R08: ffffea00010bf818 R09: 0000000000000000
R10: 0000000000000001 R11: ffff880000000000 R12: ffff880004964720
R13: ffff88002d34d700 R14: 00000000ffffffff R15: ffff88004334fd84
FS:  00007f8939347700(0000) GS:ffff880101e00000(0000) 
knlGS:0000000000000000
CS:  e033 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 000000000000001c CR3: 0000000001c0b000 CR4: 0000000000002660
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process netback/0 (pid: 1636, threadinfo ffff88004334e000, task 
ffff880043fd5fe0)
Stack:
 ffff88004334fcb8 ffffffff8141b06d ffff880000000218 ffff880042fe1200
 ffff88004334fdb8 ffffffff81543b9b ffff88004334fd84 ffff880042c59040
 ffff88004334fd68 ffff88004334fd48 ffff880000000cc0 ffffc900106c7ac0
Call Trace:
 [<ffffffff8141b06d>] notify_remote_via_irq+0xd/0x40
 [<ffffffff81543b9b>] xen_netbk_rx_action+0x73b/0x800
 [<ffffffff81544c25>] xen_netbk_kthread+0xb5/0xa60
 [<ffffffff81080050>] ? finish_task_switch+0x60/0xd0
 [<ffffffff81071fe0>] ? wake_up_bit+0x40/0x40
 [<ffffffff81544b70>] ? xen_netbk_tx_build_gops+0xa10/0xa10
 [<ffffffff81071926>] kthread+0xc6/0xd0
 [<ffffffff810037b9>] ? xen_end_context_switch+0x19/0x20
 [<ffffffff81071860>] ? kthread_freezable_should_stop+0x70/0x70
 [<ffffffff81767c7c>] ret_from_fork+0x7c/0xb0
 [<ffffffff81071860>] ? kthread_freezable_should_stop+0x70/0x70
Code: be f5 01 00 00 48 c7 c7 12 e2 99 81 e8 d9 4c c3 ff eb cd 0f 1f 80 
00 00 00 00 55 48 89 e5 39 3d c6 fd 80 00 76 0b e8 df fa ff ff <0f> b7 
40 1c c9 c3 89 f9 31 c0 48 c7 c2 27 e2 99 81 be db 00 00
RIP  [<ffffffff8141a301>] evtchn_from_irq+0x11/0x40
 RSP <ffff88004334fc98>
CR2: 000000000000001c
---[ end trace 1b5f6b359343fcfe ]---


Which leads to xenwatch being stuck in D state, which then requires us 
to reboot the host.
SysRq : Show Blocked State
  task                        PC stack   pid father
xenwatch        D ffff880101f938c0  5056    49      2 0x00000000
 ffff880101305cb8 0000000000000246 ffff8801012a0760 00000000000138c0
 ffff880101305fd8 ffff880101304010 00000000000138c0 00000000000138c0
 ffff880101305fd8 00000000000138c0 ffff8800349224e0 ffff8801012a0760
Call Trace:
 [<ffffffff8175f444>] schedule+0x24/0x70
 [<ffffffff8154698d>] xenvif_disconnect+0x7d/0x130
 [<ffffffff81071fe0>] ? wake_up_bit+0x40/0x40
 [<ffffffff81545ac4>] frontend_changed+0x214/0x660
 [<ffffffff81080050>] ? finish_task_switch+0x60/0xd0
 [<ffffffff8141fb22>] xenbus_otherend_changed+0xb2/0xc0
 [<ffffffff8175fe39>] ? _raw_spin_unlock_irqrestore+0x19/0x20
 [<ffffffff8141fd3b>] frontend_changed+0xb/0x10
 [<ffffffff8141da3a>] xenwatch_thread+0xba/0x180
 [<ffffffff81071fe0>] ? wake_up_bit+0x40/0x40
 [<ffffffff8141d980>] ? xs_watch+0x60/0x60
 [<ffffffff81071926>] kthread+0xc6/0xd0
 [<ffffffff810037b9>] ? xen_end_context_switch+0x19/0x20
 [<ffffffff81071860>] ? kthread_freezable_should_stop+0x70/0x70
 [<ffffffff81767c7c>] ret_from_fork+0x7c/0xb0
 [<ffffffff81071860>] ? kthread_freezable_should_stop+0x70/0x70

I'll give building an updated dom0 kernel a shot, but was hoping this 
rang a bell or two.
Thanks,
-Chris

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