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BUG: KCSAN: data-race in __mod_timer / expire_timers

write to 0xffff88813bc1bd88 of 8 bytes by interrupt on cpu 0:
 expire_timers+0x11e/0x260 kernel/time/timer.c:1463
 __run_timers+0x358/0x3f0 kernel/time/timer.c:1731
 run_timer_softirq+0x19/0x30 kernel/time/timer.c:1744
 __do_softirq+0x13c/0x2c3 kernel/softirq.c:343
 asm_call_irq_on_stack+0xf/0x20
 __run_on_irqstack arch/x86/include/asm/irq_stack.h:26 [inline]
 run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:77 [inline]
 do_softirq_own_stack+0x32/0x40 arch/x86/kernel/irq_64.c:77
 invoke_softirq kernel/softirq.c:226 [inline]
 __irq_exit_rcu+0xb4/0xc0 kernel/softirq.c:420
 sysvec_apic_timer_interrupt+0x74/0x90 arch/x86/kernel/apic/apic.c:1096
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:629
 native_restore_fl arch/x86/include/asm/irqflags.h:41 [inline]
 arch_local_irq_restore arch/x86/include/asm/irqflags.h:84 [inline]
 kcsan_setup_watchpoint+0x1fc/0x4d0 kernel/kcsan/core.c:591
 page_zonenum include/linux/mm.h:1101 [inline]
 is_zone_device_page include/linux/mm.h:1108 [inline]
 release_pages+0x136/0xa80 mm/swap.c:881
 free_pages_and_swap_cache+0x1db/0x1f0 mm/swap_state.c:355
 tlb_batch_pages_flush mm/mmu_gather.c:49 [inline]
 tlb_flush_mmu_free mm/mmu_gather.c:242 [inline]
 tlb_flush_mmu+0x597/0x5f0 mm/mmu_gather.c:249
 zap_pte_range+0x1168/0x13e0 mm/memory.c:1330
 zap_pmd_range mm/memory.c:1368 [inline]
 zap_pud_range mm/memory.c:1397 [inline]
 zap_p4d_range mm/memory.c:1418 [inline]
 unmap_page_range+0x560/0x660 mm/memory.c:1439
 unmap_single_vma+0x157/0x210 mm/memory.c:1484
 unmap_vmas+0xbf/0x150 mm/memory.c:1516
 exit_mmap+0x1c7/0x400 mm/mmap.c:3220
 __mmput+0xa2/0x220 kernel/fork.c:1082
 mmput+0x38/0x40 kernel/fork.c:1103
 exit_mm+0x33f/0x430 kernel/exit.c:501
 do_exit+0x41f/0x1690 kernel/exit.c:812
 do_group_exit+0x17d/0x180 kernel/exit.c:922
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:933
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:931
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:931
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88813bc1bd88 of 8 bytes by task 1948 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+0x73/0xb0 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:296

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1948 Comm: kworker/u4:3 Not tainted 5.11.0-rc6-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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