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BUG: KCSAN: data-race in del_timer / enqueue_timer

read to 0xffff8881262dfd20 of 8 bytes by task 7705 on cpu 1:
 del_timer+0x3b/0xb0 kernel/time/timer.c:1198
 try_to_grab_pending+0x22d/0x3e0 kernel/workqueue.c:1251
 __cancel_work_timer+0x53/0x340 kernel/workqueue.c:3086
 cancel_delayed_work_sync+0x24/0x40 kernel/workqueue.c:3259
 bond_free_slave+0x34/0x90 drivers/net/bonding/bond_main.c:1320
 __bond_release_one.cold+0x6e2/0x894 drivers/net/bonding/bond_main.c:2019
 bond_slave_netdev_event drivers/net/bonding/bond_main.c:3122 [inline]
 bond_netdev_event+0x4da/0x510 drivers/net/bonding/bond_main.c:3233
 notifier_call_chain+0xd7/0x160 kernel/notifier.c:95
 __raw_notifier_call_chain kernel/notifier.c:396 [inline]
 raw_notifier_call_chain+0x37/0x50 kernel/notifier.c:403
 call_netdevice_notifiers_info+0x48/0xc0 net/core/dev.c:1668
 call_netdevice_notifiers_extack net/core/dev.c:1680 [inline]
 call_netdevice_notifiers net/core/dev.c:1694 [inline]
 rollback_registered_many+0x723/0xa00 net/core/dev.c:8522
 unregister_netdevice_many net/core/dev.c:9675 [inline]
 unregister_netdevice_many+0x62/0x240 net/core/dev.c:9670
 default_device_exit_batch+0x234/0x270 net/core/dev.c:10146
 ops_exit_list.isra.0+0xa2/0xc0 net/core/net_namespace.c:175
 cleanup_net+0x405/0x6b0 net/core/net_namespace.c:597
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
 worker_thread+0xa0/0x800 kernel/workqueue.c:2415
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

write to 0xffff8881262dfd20 of 8 bytes by task 7639 on cpu 0:
 hlist_add_head include/linux/list.h:787 [inline]
 enqueue_timer+0x6c/0x210 kernel/time/timer.c:540
 __internal_add_timer+0x4f/0x60 kernel/time/timer.c:553
 internal_add_timer kernel/time/timer.c:595 [inline]
 __mod_timer kernel/time/timer.c:1053 [inline]
 mod_timer kernel/time/timer.c:1100 [inline]
 add_timer+0x250/0x550 kernel/time/timer.c:1136
 __queue_delayed_work+0x13b/0x1d0 kernel/workqueue.c:1649
 queue_delayed_work_on+0xf3/0x110 kernel/workqueue.c:1674
 queue_delayed_work include/linux/workqueue.h:509 [inline]
 batadv_nc_start_timer net/batman-adv/network-coding.c:79 [inline]
 batadv_nc_worker+0x29d/0x390 net/batman-adv/network-coding.c:740
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
 worker_thread+0xa0/0x800 kernel/workqueue.c:2415
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7639 Comm: kworker/u4:0 Not tainted 5.4.0-rc7+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: bat_events batadv_nc_worker
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