WARNING: locking bug in try_to_grab_pending

[syzbot <syzbot+2b713236b28823cd4dff@syzkaller.appspotmail.com>]

Hello,

syzbot found the following crash on:

HEAD commit:    6663cf821c13 flow_offload: Fix flow action infrastructure
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15927de4c00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8572a6e4661225f4
dashboard link: https://syzkaller.appspot.com/bug?extid=2b713236b28823cd4dff
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13e932a8c00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2b713236b28823cd4dff@syzkaller.appspotmail.com

Started in network mode
Own node identity 7f000001, cluster identity 4711
Enabled bearer <udp:syz0>, priority 10
------------[ cut here ]------------
DEBUG_LOCKS_WARN_ON(class_idx > MAX_LOCKDEP_KEYS)
WARNING: CPU: 1 PID: 3476 at kernel/locking/lockdep.c:3315  
__lock_acquire+0x13bf/0x4700 kernel/locking/lockdep.c:3315
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 3476 Comm: kworker/1:2 Not tainted 5.0.0-rc5+ #59
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue:  addrconf_dad_work (ipv6_addrconf)
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x172/0x1f0 lib/dump_stack.c:113
  panic+0x2cb/0x65c kernel/panic.c:214
  __warn.cold+0x20/0x45 kernel/panic.c:571
  report_bug+0x263/0x2b0 lib/bug.c:186
  fixup_bug arch/x86/kernel/traps.c:178 [inline]
  fixup_bug arch/x86/kernel/traps.c:173 [inline]
  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
  do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:290
  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
RIP: 0010:__lock_acquire+0x13bf/0x4700 kernel/locking/lockdep.c:3315
Code: 8b 1d e9 c7 05 08 45 85 db 0f 85 d6 f4 ff ff 48 c7 c6 a0 a4 6b 87 48  
c7 c7 00 79 6b 87 44 89 9c 24 98 00 00 00 e8 3f 2f ec ff <0f> 0b 44 8b 9c  
24 98 00 00 00 e9 af f4 ff ff 8b 3d 5c 7a fe 08 85
RSP: 0018:ffff88809b5478b0 EFLAGS: 00010086
RAX: 0000000000000000 RBX: 00000000005e00a8 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff815a8f66 RDI: ffffed10136a8f08
RBP: ffff88809b547a78 R08: ffff88809b58e680 R09: fffffbfff1133341
R10: fffffbfff1133340 R11: ffffffff88999a03 R12: ffff88809b58efb8
R13: ffff88809b58efc2 R14: 00000000005e00a8 R15: ffff88809b58e680
  lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:3841
  __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
  _raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:144
  spin_lock include/linux/spinlock.h:329 [inline]
  try_to_grab_pending+0x129/0x710 kernel/workqueue.c:1259
  __cancel_work kernel/workqueue.c:3115 [inline]
  cancel_delayed_work+0x82/0x2d0 kernel/workqueue.c:3144
  addrconf_del_dad_work+0x1c/0x50 net/ipv6/addrconf.c:312
  addrconf_dad_stop+0x129/0x2e0 net/ipv6/addrconf.c:2040
  addrconf_dad_begin net/ipv6/addrconf.c:3973 [inline]
  addrconf_dad_work+0xdbf/0x1150 net/ipv6/addrconf.c:4062
  process_one_work+0x98e/0x1790 kernel/workqueue.c:2173
  worker_thread+0x98/0xe40 kernel/workqueue.c:2319
  kthread+0x357/0x430 kernel/kthread.c:246
  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
Kernel Offset: disabled
Rebooting in 86400 seconds..


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