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BUG: KCSAN: data-race in __mod_timer / expire_timers

write to 0xffff88813bc1b908 of 8 bytes by interrupt on cpu 0:
 expire_timers+0x11e/0x260 kernel/time/timer.c:1477
 __run_timers+0x358/0x3f0 kernel/time/timer.c:1745
 run_timer_softirq+0x19/0x30 kernel/time/timer.c:1758
 __do_softirq+0x13c/0x2c3 kernel/softirq.c:345
 invoke_softirq kernel/softirq.c:221 [inline]
 __irq_exit_rcu+0xb4/0xc0 kernel/softirq.c:422
 sysvec_apic_timer_interrupt+0x6e/0x80 arch/x86/kernel/apic/apic.c:1100
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:632
 _raw_spin_lock+0x0/0x50 kernel/locking/spinlock.c:143
 spin_lock include/linux/spinlock.h:354 [inline]
 finish_fault+0x381/0x490 mm/memory.c:3815
 do_read_fault+0x324/0x530 mm/memory.c:3943
 do_fault mm/memory.c:4067 [inline]
 handle_pte_fault mm/memory.c:4318 [inline]
 __handle_mm_fault mm/memory.c:4453 [inline]
 handle_mm_fault+0x1019/0x1840 mm/memory.c:4551
 faultin_page mm/gup.c:850 [inline]
 __get_user_pages+0xa47/0x1000 mm/gup.c:1069
 populate_vma_page_range mm/gup.c:1402 [inline]
 __mm_populate+0x24d/0x380 mm/gup.c:1450
 mm_populate include/linux/mm.h:2570 [inline]
 do_shmat+0x727/0x940 ipc/shm.c:1567
 __do_sys_shmat ipc/shm.c:1594 [inline]
 __se_sys_shmat ipc/shm.c:1589 [inline]
 __x64_sys_shmat+0x58/0xa0 ipc/shm.c:1589
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88813bc1b908 of 8 bytes by task 263 on cpu 1:
 __mod_timer+0x44e/0xc10 kernel/time/timer.c:1035
 add_timer+0x38/0x50 kernel/time/timer.c:1142
 __queue_delayed_work+0xec/0x150 kernel/workqueue.c:1655
 queue_delayed_work_on+0x6f/0xd0 kernel/workqueue.c:1680
 queue_delayed_work include/linux/workqueue.h:522 [inline]
 batadv_bla_periodic_work+0x529/0x590 net/batman-adv/bridge_loop_avoidance.c:1508
 process_one_work+0x3e1/0x950 kernel/workqueue.c:2275
 worker_thread+0x616/0xa70 kernel/workqueue.c:2421
 kthread+0x20b/0x230 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 263 Comm: kworker/u4:3 Not tainted 5.12.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: bat_events batadv_bla_periodic_work
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