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BUG: KCSAN: data-race in add_timer_on / timer_clear_idle

read to 0xffff88812c01daa4 of 1 bytes by interrupt on cpu 1:
 forward_timer_base kernel/time/timer.c:892 [inline]
 add_timer_on+0x20e/0x2d0 kernel/time/timer.c:1171
 clocksource_watchdog+0x63f/0x760 kernel/time/clocksource.c:297
 call_timer_fn+0x5f/0x2f0 kernel/time/timer.c:1404
 expire_timers kernel/time/timer.c:1449 [inline]
 __run_timers kernel/time/timer.c:1773 [inline]
 __run_timers kernel/time/timer.c:1740 [inline]
 run_timer_softirq+0xc0c/0xcd0 kernel/time/timer.c:1786
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 invoke_softirq kernel/softirq.c:373 [inline]
 irq_exit+0xbb/0xe0 kernel/softirq.c:413
 exiting_irq arch/x86/include/asm/apic.h:536 [inline]
 smp_apic_timer_interrupt+0xe6/0x280 arch/x86/kernel/apic/apic.c:1137
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
 arch_local_irq_restore arch/x86/include/asm/paravirt.h:752 [inline]
 kcsan_setup_watchpoint+0x1d4/0x460 kernel/kcsan/core.c:429
 check_access kernel/kcsan/core.c:459 [inline]
 __tsan_read8+0xc6/0x100 kernel/kcsan/core.c:589
 __do_sys_nanosleep kernel/time/hrtimer.c:1956 [inline]
 __se_sys_nanosleep kernel/time/hrtimer.c:1948 [inline]
 __x64_sys_nanosleep+0x6f/0x150 kernel/time/hrtimer.c:1948
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff88812c01daa4 of 1 bytes by task 0 on cpu 0:
 timer_clear_idle+0x42/0x50 kernel/time/timer.c:1675
 tick_nohz_next_event+0x15d/0x370 kernel/time/tick-sched.c:719
 __tick_nohz_idle_stop_tick kernel/time/tick-sched.c:954 [inline]
 tick_nohz_idle_stop_tick+0x3c2/0x670 kernel/time/tick-sched.c:984
 cpuidle_idle_call kernel/sched/idle.c:151 [inline]
 do_idle+0x1b8/0x290 kernel/sched/idle.c:269
 cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:361
 rest_init+0xec/0xf6 init/main.c:452
 arch_call_rest_init+0x17/0x37
 start_kernel+0x838/0x85e init/main.c:786
 x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:490
 x86_64_start_kernel+0x72/0x76 arch/x86/kernel/head64.c:471
 secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:242

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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