WARNING in batadv_mcast_mla_tt_retract

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    eed9688f8513 Merge branch 'ras-core-for-linus' of git://gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=103bffaf400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fa5c63e12fd85b25
dashboard link: https://syzkaller.appspot.com/bug?extid=83f2d54ec6b7e417e13f
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+83f2d54ec6b7e417e13f@xxxxxxxxxxxxxxxxxxxxxxxxx

bond0 (unregistering): Releasing backup interface bond_slave_0
bond0 (unregistering): Released all slaves
WARNING: CPU: 1 PID: 7 at net/batman-adv/multicast.c:337  
batadv_mcast_mla_tt_retract+0x476/0x590 net/batman-adv/multicast.c:337
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 7 Comm: kworker/u4:0 Not tainted 4.20.0+ #169
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: bat_events batadv_mcast_mla_update
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1d3/0x2c6 lib/dump_stack.c:113
 panic+0x2ad/0x55c kernel/panic.c:188
 __warn.cold.8+0x20/0x45 kernel/panic.c:540
 report_bug+0x254/0x2d0 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:178 [inline]
 do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
 do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:290
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
RIP: 0010:batadv_mcast_mla_tt_retract+0x476/0x590  
net/batman-adv/multicast.c:337
Code: 00 00 ad de 4c 89 ff 49 89 47 08 e8 b4 0f 03 fa e9 b6 fe ff ff 49 8d  
47 10 48 89 85 60 ff ff ff e9 05 ff ff ff e8 4a 30 c0 f9 <0f> 0b e9 3f fc  
ff ff e8 6e 3b 03 fa e9 44 fe ff ff 4c 89 f7 e8 81
RSP: 0018:ffff8880a9e1f260 EFLAGS: 00010293
RAX: ffff8880a9e041c0 RBX: 0000000000000001 RCX: ffffffff87bedca3
RDX: 0000000000000000 RSI: ffffffff87bee066 RDI: 0000000000000007
RBP: ffff8880a9e1f328 R08: ffff8880a9e041c0 R09: ffffed1015ce5b8f
R10: 0000000000000003 R11: ffff8880ae72dc7b R12: ffff8880a9e1f490
R13: 0000000000000000 R14: ffff888055b95fc0 R15: ffff8880a9e1f710
 __batadv_mcast_mla_update net/batman-adv/multicast.c:635 [inline]
 batadv_mcast_mla_update+0x819/0x2da0 net/batman-adv/multicast.c:661
 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
Kernel Offset: disabled
Rebooting in 86400 seconds..


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