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[Bug 1011792] Re: Kernel lockup running 3.0.0 and 3.2.0 on multiple EC2 instance types

 

** Branch linked: lp:ubuntu/lucid-proposed/linux-lts-backport-oneiric

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https://bugs.launchpad.net/bugs/1011792

Title:
  Kernel lockup running 3.0.0 and 3.2.0 on multiple EC2 instance types

Status in “linux” package in Ubuntu:
  Fix Released
Status in “linux-lts-backport-oneiric” package in Ubuntu:
  Invalid
Status in “linux” source package in Lucid:
  Fix Released
Status in “linux-lts-backport-oneiric” source package in Lucid:
  Fix Released
Status in “linux” source package in Oneiric:
  Fix Released
Status in “linux-lts-backport-oneiric” source package in Oneiric:
  Confirmed
Status in “linux” source package in Precise:
  Fix Released
Status in “linux-lts-backport-oneiric” source package in Precise:
  Invalid
Status in “linux” source package in Quantal:
  Fix Released
Status in “linux-lts-backport-oneiric” source package in Quantal:
  Invalid
Status in “linux” source package in Raring:
  Fix Released
Status in “linux-lts-backport-oneiric” source package in Raring:
  Invalid

Bug description:
  SRU Justification:

  Impact: Running lots of threads which utilize spinlocks (the pgslam
  testcase is quite successful in causing this), we hit a stage where
  the spinlock is still locked but none of the CPUs seem to be actively
  holding it. The reason for this is not yet completely understood. From
  evidence it looks like at least one CPU tries to get the lock, fails
  and goes into the pv-spinlocks special case of doing a hv call. This
  call seems to return, but somehow not to where it left, so the lock is
  never taken and other cpus are sometimes stuck in the hv call.

  Fix: This problem seems to be avoidable by not enabling the cpu
  interrupts/event channel before doing the hv call. This may have some
  performance penalties but on the other hand testing did not seem to be
  much worse and does actually survive the run.

  Testcase: pgslam test script below.

  ---

  Scheduler deadlocks have been observed on c1.xlarge EC2 instances
  running 10.04.3 LTS with the  3.0.0-20-virtual Oneiric backport
  kernel. The symptoms appear similar to bug 929941, where multiple CPUs
  are waiting on scheduler runqueue locks. But in this case, only a few
  CPUs are stuck.

  A typical set of stack traces from the guest state looks like:

  VCPU0
  rip: ffffffff810013aa hypercall_page+0x3aa
  flags: 00001202 i nz
  rsp: ffff8801b3c27910
  rax: 0000000000000000   rcx: ffffffff810013aa   rdx: ffff8801b3c27954
  rbx: ffff88000265cb30   rsi: ffff8801b3c27938   rdi: 0000000000000003
  rbp: ffff8801b3c27958    r8: 0000000000000001    r9: 0000000000000001
  r10: 0000000000000000   r11: 0000000000000202   r12: 0000000000000011
  r13: 0000000000000001   r14: 0000000000000001   r15: 0000000000000000
   cs: e033        ss: e02b        ds: 0000        es: 0000
   fs: 0000 @ 00007f4ce223f700
   gs: 0000 @ ffff8801bfed4000/0000000000000000

  cr0: 80050033
  cr2: 0061ade0
  cr3: 0e93d000
  cr4: 00002660

  dr0: 00000000
  dr1: 00000000
  dr2: 00000000
  dr3: 00000000
  dr6: ffff0ff0
  dr7: 00000400
  Code (instr addr ffffffff810013aa)
  cc cc cc cc cc cc cc cc cc cc cc 51 41 53 b8 1d 00 00 00 0f 05 <41> 5b 59 c3 cc cc cc cc cc cc cc

  Stack:
   0000000000000246 0000000000000000 ffffffff81394b42 ffff8801b3c27938
   0000000000000000 ffff8801b3c27954 ffffffff00000001 0000000000000000
   0000000481394ad6 ffff8801b3c27968 ffffffff81394b60 ffff8801b3c279b8
   ffffffff8100933f ffff8801b3c27a48 0000000000000000 ffff8801b3c27998

  Call Trace:
    [<ffffffff810013aa>] hypercall_page+0x3aa  <--
    [<ffffffff81394b42>] xen_poll_irq_timeout+0x42
    [<ffffffff81394b60>] xen_poll_irq+0x10
    [<ffffffff8100933f>] xen_spin_lock_slow+0x7f
    [<ffffffff81009435>] xen_spin_lock_flags+0x75
    [<ffffffff8160365f>] _raw_spin_lock_irqsave+0x2f
    [<ffffffff8104ee50>] task_rq_lock+0x40
    [<ffffffff8104f069>] task_sched_runtime+0x29
    [<ffffffff81085f38>] thread_group_cputime+0x88
    [<ffffffff812c4dc9>] apparmor_ptrace_access_check+0x39
    [<ffffffff81051593>] thread_group_times+0x33
    [<ffffffff811d4192>] do_task_stat+0x6d2
    [<ffffffff8160361e>] _raw_spin_lock+0xe
    [<ffffffff8119165f>] seq_open+0x4f
    [<ffffffff811d0380>] sched_autogroup_show+0x70
    [<ffffffff811d0380>] sched_autogroup_show+0x70
    [<ffffffff8119173a>] single_open+0x7a
    [<ffffffff811cdbf0>] sched_open+0x20
    [<ffffffff811cdc0b>] proc_single_open+0x1b
    [<ffffffff8118e460>] mntput_no_expire+0x60
    [<ffffffff8118e5ad>] mntput+0x1d
    [<ffffffff811d4624>] proc_tgid_stat+0x14
    [<ffffffff811d03e1>] proc_single_show+0x61
    [<ffffffff81191be2>] seq_read+0xf2
    [<ffffffff8116fe35>] vfs_read+0xc5
    [<ffffffff81170001>] sys_read+0x51
    [<ffffffff8160ba02>] system_call_fastpath+0x16

  VCPU1
  rip: ffffffff8105a777 try_to_wake_up+0xd7
  flags: 00001202 i nz
  rsp: ffff8801bfef28f0
  rax: 0000000000000003   rcx: 0000000000000000   rdx: 0000000000000001
  rbx: 0000000000012980   rsi: ffff8801b1990078   rdi: 0000000000000000
  rbp: ffff8801bfef2950    r8: 0000000000000000    r9: 0000000000000000
  r10: 0000000000000000   r11: 00000000fb981853   r12: ffff88000265c530
  r13: 0000000000000000   r14: ffff88000265cb30   r15: 0000000000000000
   cs: e033        ss: e02b        ds: 0000        es: 0000
   fs: 0000 @ 00007ff68926c700
   gs: 0000 @ ffff8801bfeef000/0000000000000000

  cr0: 8005003b
  cr2: 00441d80
  cr3: 1174cb000
  cr4: 00002660

  dr0: 00000000
  dr1: 00000000
  dr2: 00000000
  dr3: 00000000
  dr6: ffff0ff0
  dr7: 00000400
  Code (instr addr ffffffff8105a777)
  00 00 eb 0c 66 2e 0f 1f 84 00 00 00 00 00 f3 90 41 8b 54 24 28 <85> d2 75 f5 49 8b 14 24 31 c0 83

  Stack:
   0000000000000000 ffff8801b41d2858 ffff8801bfef2950 ffffffff8153e51e
   0000000300000004 ffff8801b1990078 ffff8801bfef2930 ffff8800026f6c18
   0000000000000001 ffff8800026f6c30 0000000000000000 0000000000000000
   ffff8801bfef2960 ffffffff8105a962 ffff8801bfef29b0 ffffffff81049709

  Call Trace:
    [<ffffffff8105a777>] try_to_wake_up+0xd7  <--
    [<ffffffff8153e51e>] ip_finish_output+0x16e
    [<ffffffff8105a962>] default_wake_function+0x12
    [<ffffffff81049709>] __wake_up_common+0x59
    [<ffffffff81049758>] __wake_up_locked+0x18
    [<ffffffff811afcf4>] ep_poll_callback+0xa4
    [<ffffffff81049709>] __wake_up_common+0x59
    [<ffffffff8104ed53>] __wake_up_sync_key+0x53
    [<ffffffff814f3d2e>] sock_def_readable+0x3e
    [<ffffffff8155255a>] tcp_rcv_established+0x26a
    [<ffffffff8100742d>] xen_force_evtchn_callback+0xd
    [<ffffffff81007b72>] check_events+0x12
    [<ffffffff8155a9a5>] tcp_v4_do_rcv+0x125
    [<ffffffff8155c169>] tcp_v4_rcv+0x5a9
    [<ffffffff8153854d>] ip_local_deliver_finish+0xdd
    [<ffffffff81538790>] ip_local_deliver+0x80
    [<ffffffff81537db9>] ip_rcv_finish+0x119
    [<ffffffff815383a8>] ip_rcv+0x228
    [<ffffffff815d0afd>] packet_rcv_spkt+0x4d
    [<ffffffff815036b0>] __netif_receive_skb+0x1e0
    [<ffffffff81506790>] netif_receive_skb+0x80
    [<ffffffff814614f4>] handle_incoming_queue+0x134
    [<ffffffff81461fd7>] xennet_poll+0x277
    [<ffffffff81506ff8>] net_rx_action+0x108
    [<ffffffff8160361e>] _raw_spin_lock+0xe
    [<ffffffff8106889f>] __do_softirq+0xbf
    [<ffffffff810d3f7d>] handle_edge_irq+0x9d
    [<ffffffff8160cc1c>] call_softirq+0x1c
    [<ffffffff8100d3d5>] do_softirq+0x65
    [<ffffffff8106869d>] irq_exit+0xbd
    [<ffffffff81394ee5>] xen_evtchn_do_upcall+0x35
    [<ffffffff8160cc6e>] xen_do_hypervisor_callback+0x1e

  VCPU2
  rip: ffffffff810013aa hypercall_page+0x3aa
  flags: 00001202 i nz
  rsp: ffff8801bff0da00
  rax: 0000000000000000   rcx: ffffffff810013aa   rdx: ffff8801bff0da44
  rbx: ffff8800026f6c00   rsi: ffff8801bff0da28   rdi: 0000000000000003
  rbp: ffff8801bff0da48    r8: 00000000000000c3    r9: 000000000000c110
  r10: 0000000000100000   r11: 0000000000000202   r12: 000000000000001d
  r13: 0000000000000001   r14: 0000000000000001   r15: 0000000000000000
   cs: e033        ss: e02b        ds: 0000        es: 0000
   fs: 0000 @ 00007f408128b700
   gs: 0000 @ ffff8801bff0a000/0000000000000000

  cr0: 80050033
  cr2: 0061ade0
  cr3: 289f2000
  cr4: 00002660

  dr0: 00000000
  dr1: 00000000
  dr2: 00000000
  dr3: 00000000
  dr6: ffff0ff0
  dr7: 00000400
  Code (instr addr ffffffff810013aa)
  cc cc cc cc cc cc cc cc cc cc cc 51 41 53 b8 1d 00 00 00 0f 05 <41> 5b 59 c3 cc cc cc cc cc cc cc

  Stack:
   0000000000112000 0000000000000000 ffffffff81394b42 ffff8801bff0da28
   0000000000000000 ffff8801bff0da44 ffffffff00000001 0000000000000000
   0000001081394ad6 ffff8801bff0da58 ffffffff81394b60 ffff8801bff0daa8
   ffffffff8100933f ffff8801bff0da88 0000000000000000 ffff8801b3d14530

  Call Trace:
    [<ffffffff810013aa>] hypercall_page+0x3aa  <--
    [<ffffffff81394b42>] xen_poll_irq_timeout+0x42
    [<ffffffff81394b60>] xen_poll_irq+0x10
    [<ffffffff8100933f>] xen_spin_lock_slow+0x7f
    [<ffffffff81009435>] xen_spin_lock_flags+0x75
    [<ffffffff8160365f>] _raw_spin_lock_irqsave+0x2f
    [<ffffffff811afca9>] ep_poll_callback+0x59
    [<ffffffff816036ae>] _raw_spin_unlock_irqrestore+0x1e
    [<ffffffff81049709>] __wake_up_common+0x59
    [<ffffffff8104ed53>] __wake_up_sync_key+0x53
    [<ffffffff814f3d2e>] sock_def_readable+0x3e
    [<ffffffff8154ef50>] tcp_data_queue+0x300
    [<ffffffff81552639>] tcp_rcv_established+0x349
    [<ffffffff8155a9a5>] tcp_v4_do_rcv+0x125
    [<ffffffff8155c169>] tcp_v4_rcv+0x5a9
    [<ffffffff81054e18>] enqueue_sleeper+0x188
    [<ffffffff8153854d>] ip_local_deliver_finish+0xdd
    [<ffffffff81538790>] ip_local_deliver+0x80
    [<ffffffff81537db9>] ip_rcv_finish+0x119
    [<ffffffff815383a8>] ip_rcv+0x228
    [<ffffffff815036b0>] __netif_receive_skb+0x1e0
    [<ffffffff81007b5f>] xen_restore_fl_direct_reloc+0x4
    [<ffffffff810d7af4>] rcu_enter_nohz+0x44
    [<ffffffff81503aeb>] process_backlog+0x10b
    [<ffffffff810d10b5>] handle_irq_event_percpu+0xb5
    [<ffffffff81506ff8>] net_rx_action+0x108
    [<ffffffff8100742d>] xen_force_evtchn_callback+0xd
    [<ffffffff8106889f>] __do_softirq+0xbf
    [<ffffffff81007b5f>] xen_restore_fl_direct_reloc+0x4
    [<ffffffff8160cc1c>] call_softirq+0x1c

  VCPU3
  rip: ffffffff810013aa hypercall_page+0x3aa
  flags: 00001202 i nz
  rsp: ffff8801b1993b10
  rax: 0000000000000000   rcx: ffffffff810013aa   rdx: ffff8801b1993b54
  rbx: ffff8801bff01980   rsi: ffff8801b1993b38   rdi: 0000000000000003
  rbp: ffff8801b1993b58    r8: ffff8801bf004760    r9: 0000000000000040
  r10: 000000000000001d   r11: 0000000000000202   r12: 0000000000000023
  r13: 0000000000000001   r14: 0000000000000001   r15: 0000000000000000
   cs: e033        ss: e02b        ds: 0000        es: 0000
   fs: 0000 @ 00007f1a15c06700
   gs: 0000 @ ffff8801bff25000/0000000000000000

  cr0: 80050033
  cr2: 7f78b037de20
  cr3: 0e9c9000
  cr4: 00002660

  dr0: 00000000
  dr1: 00000000
  dr2: 00000000
  dr3: 00000000
  dr6: ffff0ff0
  dr7: 00000400
  Code (instr addr ffffffff810013aa)
  cc cc cc cc cc cc cc cc cc cc cc 51 41 53 b8 1d 00 00 00 0f 05 <41> 5b 59 c3 cc cc cc cc cc cc cc

  Stack:
   0000000000000001 0000000000000000 ffffffff81394b42 ffff8801b1993b38
   0000000000000000 ffff8801b1993b54 ffffffff00000001 0000000000000000
   0000001681394ad6 ffff8801b1993b68 ffffffff81394b60 ffff8801b1993bb8
   ffffffff8100933f 0000000000000000 0000000000000000 0000000000000000

  Call Trace:
    [<ffffffff810013aa>] hypercall_page+0x3aa  <--
    [<ffffffff81394b42>] xen_poll_irq_timeout+0x42
    [<ffffffff81394b60>] xen_poll_irq+0x10
    [<ffffffff8100933f>] xen_spin_lock_slow+0x7f
    [<ffffffff81009496>] xen_spin_lock+0x56
    [<ffffffff8160361e>] _raw_spin_lock+0xe
    [<ffffffff8104d90d>] double_rq_lock+0x2d
    [<ffffffff81059f15>] load_balance+0x1f5
    [<ffffffff81601576>] __schedule+0x7e6
    [<ffffffff8160165f>] schedule+0x3f
    [<ffffffff816025b5>] schedule_hrtimeout_range_clock+0xc5
    [<ffffffff810881c0>] update_rmtp+0x80
    [<ffffffff81089524>] hrtimer_start_range_ns+0x14
    [<ffffffff81602663>] schedule_hrtimeout_range+0x13
    [<ffffffff811af9f8>] ep_poll+0x2d8
    [<ffffffff8105a950>] try_to_wake_up+0x2b0
    [<ffffffff81290c2b>] security_file_permission+0x8b
    [<ffffffff8116fee0>] vfs_read+0x170
    [<ffffffff811afb35>] sys_epoll_wait+0xc5
    [<ffffffff8160ba02>] system_call_fastpath+0x16

  VCPU4
  rip: ffffffff810013aa hypercall_page+0x3aa
  flags: 00001246 i z p
  rsp: ffff8801b45f5ed8
  rax: 0000000000000000   rcx: ffffffff810013aa   rdx: 0000000000000000
  rbx: ffff8801b45f4010   rsi: 0000000000000000   rdi: 0000000000000001
  rbp: ffff8801b45f5ef0    r8: 0000000000000000    r9: 0000000000000000
  r10: 0000000000000000   r11: 0000000000000246   r12: 0000000000000004
  r13: 0000000000000000   r14: 0000000000000000   r15: 0000000000000000
   cs: e033        ss: e02b        ds: 002b        es: 002b
   fs: 0000 @ 00007fe085364700
   gs: 0000 @ ffff8801bff40000/0000000000000000

  cr0: 8005003b
  cr2: 7f7127c10000
  cr3: 29c76000
  cr4: 00002660

  dr0: 00000000
  dr1: 00000000
  dr2: 00000000
  dr3: 00000000
  dr6: ffff0ff0
  dr7: 00000400
  Code (instr addr ffffffff810013aa)
  cc cc cc cc cc cc cc cc cc cc cc 51 41 53 b8 1d 00 00 00 0f 05 <41> 5b 59 c3 cc cc cc cc cc cc cc

  Stack:
   0000000000000000 0000000000000000 ffffffff81007490 ffff8801b45f5f10
   ffffffff81013c3d ffff8801b45f4010 ffffffff81cc7f48 ffff8801b45f5f40
   ffffffff8100b0c7 ffffffff81007b19 6811f30c74562efe 0000000000000000
   0000000000000000 ffff8801b45f5f50 ffffffff815f523d 0000000000000000

  Call Trace:
    [<ffffffff810013aa>] hypercall_page+0x3aa  <--
    [<ffffffff81007490>] xen_safe_halt+0x10
    [<ffffffff81013c3d>] default_idle+0x5d
    [<ffffffff8100b0c7>] cpu_idle+0xb7
    [<ffffffff81007b19>] xen_irq_enable_direct_reloc+0x4
    [<ffffffff815f523d>] cpu_bringup_and_idle+0xe

  VCPU5
  rip: ffffffff810013aa hypercall_page+0x3aa
  flags: 00001246 i z p
  rsp: ffff8801b45f7ed8
  rax: 0000000000000000   rcx: ffffffff810013aa   rdx: 0000000000000000
  rbx: ffff8801b45f6010   rsi: 0000000000000000   rdi: 0000000000000001
  rbp: ffff8801b45f7ef0    r8: 0000000000000000    r9: 0000000000000000
  r10: 0000000000000000   r11: 0000000000000246   r12: 0000000000000005
  r13: 0000000000000000   r14: 0000000000000000   r15: 0000000000000000
   cs: e033        ss: e02b        ds: 002b        es: 002b
   fs: 0000 @ 00007fcf9cf7a700
   gs: 0000 @ ffff8801bff5b000/0000000000000000

  cr0: 8005003b
  cr2: 7faf54aac360
  cr3: 325e8000
  cr4: 00002660

  dr0: 00000000
  dr1: 00000000
  dr2: 00000000
  dr3: 00000000
  dr6: ffff0ff0
  dr7: 00000400
  Code (instr addr ffffffff810013aa)
  cc cc cc cc cc cc cc cc cc cc cc 51 41 53 b8 1d 00 00 00 0f 05 <41> 5b 59 c3 cc cc cc cc cc cc cc

  Stack:
   0000000000000000 0000000000000000 ffffffff81007490 ffff8801b45f7f10
   ffffffff81013c3d ffff8801b45f6010 ffffffff81cc7f48 ffff8801b45f7f40
   ffffffff8100b0c7 ffffffff81007b19 afec8dc6140892fe 0000000000000000
   0000000000000000 ffff8801b45f7f50 ffffffff815f523d 0000000000000000

  Call Trace:
    [<ffffffff810013aa>] hypercall_page+0x3aa  <--
    [<ffffffff81007490>] xen_safe_halt+0x10
    [<ffffffff81013c3d>] default_idle+0x5d
    [<ffffffff8100b0c7>] cpu_idle+0xb7
    [<ffffffff81007b19>] xen_irq_enable_direct_reloc+0x4
    [<ffffffff815f523d>] cpu_bringup_and_idle+0xe

  VCPU6
  rip: ffffffff810013aa hypercall_page+0x3aa
  flags: 00001246 i z p
  rsp: ffff8801b4601ed8
  rax: 0000000000000000   rcx: ffffffff810013aa   rdx: 0000000000000000
  rbx: ffff8801b4600010   rsi: 0000000000000000   rdi: 0000000000000001
  rbp: ffff8801b4601ef0    r8: 0000000000000000    r9: 0000000000000000
  r10: 0000000000000000   r11: 0000000000000246   r12: 0000000000000006
  r13: 0000000000000000   r14: 0000000000000000   r15: 0000000000000000
   cs: e033        ss: e02b        ds: 002b        es: 002b
   fs: 0000 @ 00007ff5deb9b700
   gs: 0000 @ ffff8801bff76000/0000000000000000

  cr0: 8005003b
  cr2: 7faf5345dff8
  cr3: 10160000
  cr4: 00002660

  dr0: 00000000
  dr1: 00000000
  dr2: 00000000
  dr3: 00000000
  dr6: ffff0ff0
  dr7: 00000400
  Code (instr addr ffffffff810013aa)
  cc cc cc cc cc cc cc cc cc cc cc 51 41 53 b8 1d 00 00 00 0f 05 <41> 5b 59 c3 cc cc cc cc cc cc cc

  Stack:
   0000000000000000 0000000000000000 ffffffff81007490 ffff8801b4601f10
   ffffffff81013c3d ffff8801b4600010 ffffffff81cc7f48 ffff8801b4601f40
   ffffffff8100b0c7 ffffffff81007b19 f6fcdef4e1be86f4 0000000000000000
   0000000000000000 ffff8801b4601f50 ffffffff815f523d 0000000000000000

  Call Trace:
    [<ffffffff810013aa>] hypercall_page+0x3aa  <--
    [<ffffffff81007490>] xen_safe_halt+0x10
    [<ffffffff81013c3d>] default_idle+0x5d
    [<ffffffff8100b0c7>] cpu_idle+0xb7
    [<ffffffff81007b19>] xen_irq_enable_direct_reloc+0x4
    [<ffffffff815f523d>] cpu_bringup_and_idle+0xe

  VCPU7
  rip: ffffffff810013aa hypercall_page+0x3aa
  flags: 00001246 i z p
  rsp: ffff8801b4603ed8
  rax: 0000000000000000   rcx: ffffffff810013aa   rdx: 0000000000000000
  rbx: ffff8801b4602010   rsi: 0000000000000000   rdi: 0000000000000001
  rbp: ffff8801b4603ef0    r8: 0000000000000000    r9: 0000000000000000
  r10: 0000000000000000   r11: 0000000000000246   r12: 0000000000000007
  r13: 0000000000000000   r14: 0000000000000000   r15: 0000000000000000
   cs: e033        ss: e02b        ds: 002b        es: 002b
   fs: 0000 @ 00007fe081751700
   gs: 0000 @ ffff8801bff91000/0000000000000000

  cr0: 8005003b
  cr2: 7faf54bdfde0
  cr3: 29c76000
  cr4: 00002660

  dr0: 00000000
  dr1: 00000000
  dr2: 00000000
  dr3: 00000000
  dr6: ffff0ff0
  dr7: 00000400
  Code (instr addr ffffffff810013aa)
  cc cc cc cc cc cc cc cc cc cc cc 51 41 53 b8 1d 00 00 00 0f 05 <41> 5b 59 c3 cc cc cc cc cc cc cc

  Stack:
   0000000000000000 0000000000000000 ffffffff81007490 ffff8801b4603f10
   ffffffff81013c3d ffff8801b4602010 ffffffff81cc7f48 ffff8801b4603f40
   ffffffff8100b0c7 ffffffff81007b19 0c1d63da394a80a3 0000000000000000
   0000000000000000 ffff8801b4603f50 ffffffff815f523d 0000000000000000

  Call Trace:
    [<ffffffff810013aa>] hypercall_page+0x3aa  <--
    [<ffffffff81007490>] xen_safe_halt+0x10
    [<ffffffff81013c3d>] default_idle+0x5d
    [<ffffffff8100b0c7>] cpu_idle+0xb7
    [<ffffffff81007b19>] xen_irq_enable_direct_reloc+0x4
    [<ffffffff815f523d>] cpu_bringup_and_idle+0xe

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