INFO: rcu detected stall in xfrm_hash_rebuild

[syzbot <syzbot+592df0494801b6648ec6@syzkaller.appspotmail.com>]

Hello,

syzbot found the following crash on:

HEAD commit:    74c4a24df7ca Add linux-next specific files for 20181207
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17dbb3d5400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6e9413388bf37bed
dashboard link: https://syzkaller.appspot.com/bug?extid=592df0494801b6648ec6
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+592df0494801b6648ec6@syzkaller.appspotmail.com

device bridge_slave_1 entered promiscuous mode
IPv6: ADDRCONF(NETDEV_UP): veth0_to_bridge: link is not ready
IPv6: ADDRCONF(NETDEV_UP): veth1_to_bridge: link is not ready
bond0: Enslaving bond_slave_0 as an active interface with an up link
bond0: Enslaving bond_slave_1 as an active interface with an up link
rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-....: (1 GPs behind) idle=3e2/1/0x4000000000000002  
softirq=136882/136885 fqs=5250
rcu: 	 (t=10501 jiffies g=189801 q=2008)
NMI backtrace for cpu 1
CPU: 1 PID: 6200 Comm: kworker/1:2 Not tainted 4.20.0-rc5-next-20181207+  
#163
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: events xfrm_hash_rebuild
Call Trace:
  <IRQ>
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x244/0x39d lib/dump_stack.c:113
  nmi_cpu_backtrace.cold.2+0x5c/0xa1 lib/nmi_backtrace.c:101
  nmi_trigger_cpumask_backtrace+0x1e8/0x22a lib/nmi_backtrace.c:62
  arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
  trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
  rcu_dump_cpu_stacks+0x16f/0x1bc kernel/rcu/tree.c:1211
  print_cpu_stall.cold.70+0x218/0x40a kernel/rcu/tree.c:1348
  check_cpu_stall kernel/rcu/tree.c:1422 [inline]
  rcu_pending kernel/rcu/tree.c:3018 [inline]
  rcu_check_callbacks+0xf3b/0x13f0 kernel/rcu/tree.c:2521
  update_process_times+0x2d/0x70 kernel/time/timer.c:1635
  tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:161
  tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1271
  __run_hrtimer kernel/time/hrtimer.c:1389 [inline]
  __hrtimer_run_queues+0x41c/0x10d0 kernel/time/hrtimer.c:1451
  hrtimer_interrupt+0x313/0x780 kernel/time/hrtimer.c:1509
  local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1034 [inline]
  smp_apic_timer_interrupt+0x1a1/0x760 arch/x86/kernel/apic/apic.c:1059
  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:804
  </IRQ>
RIP: 0010:__read_once_size include/linux/compiler.h:182 [inline]
RIP: 0010:check_kcov_mode kernel/kcov.c:69 [inline]
RIP: 0010:write_comp_data+0x22/0x70 kernel/kcov.c:122
Code: 90 90 90 90 90 90 90 90 55 48 89 e5 65 4c 8b 04 25 40 ee 01 00 65 8b  
05 7c f6 81 7e a9 00 01 1f 00 75 51 41 8b 80 d8 12 00 00 <83> f8 03 75 45  
49 8b 80 e0 12 00 00 45 8b 80 dc 12 00 00 4c 8b 08
RSP: 0018:ffff8881872f7320 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 0000000000000000 RBX: 0000000000000003 RCX: ffffffff86d1d8db
RDX: 0000000000000003 RSI: 000000000000000e RDI: 0000000000000005
RBP: ffff8881872f7320 R08: ffff8881872ea1c0 R09: 0000000000000008
R10: 0000000000000005 R11: ffff8881872ea1c0 R12: dffffc0000000000
R13: ffff8881b628ca14 R14: ffff8881b4050114 R15: 0000000000000000
  __sanitizer_cov_trace_const_cmp4+0x16/0x20 kernel/kcov.c:188
  selector_cmp net/xfrm/xfrm_policy.c:1390 [inline]
  xfrm_policy_insert_list+0x62b/0x1020 net/xfrm/xfrm_policy.c:1534
  xfrm_policy_inexact_insert+0x166/0xee0 net/xfrm/xfrm_policy.c:1195
  xfrm_hash_rebuild+0xfba/0x1380 net/xfrm/xfrm_policy.c:1317
  process_one_work+0xc90/0x1c40 kernel/workqueue.c:2153
  worker_thread+0x17f/0x1390 kernel/workqueue.c:2296
  kthread+0x35a/0x440 kernel/kthread.c:246
  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352


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