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BUG: KCSAN: data-race in enqueue_timer / timer_reduce

read to 0xffff8881008e9b18 of 8 bytes by task 18509 on cpu 1:
 __mod_timer kernel/time/timer.c:963 [inline]
 timer_reduce+0x5d/0x830 kernel/time/timer.c:1115
 cgroup_file_notify+0x11f/0x130 kernel/cgroup/cgroup.c:4097
 pids_can_fork+0x176/0x1b0 kernel/cgroup/pids.c:233
 cgroup_can_fork+0xde/0x1b0 kernel/cgroup/cgroup.c:5881
 copy_process+0x263b/0x3c40 kernel/fork.c:2175
 _do_fork+0xfe/0x7a0 kernel/fork.c:2421
 __do_sys_clone kernel/fork.c:2576 [inline]
 __se_sys_clone kernel/fork.c:2557 [inline]
 __x64_sys_clone+0x130/0x170 kernel/fork.c:2557
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff8881008e9b18 of 8 bytes by interrupt 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
 dsp_cmx_send+0x8cd/0xcf0 drivers/isdn/mISDN/dsp_cmx.c:1850
 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]
 console_unlock+0x8fa/0xb80 kernel/printk/printk.c:2481
 vprintk_emit+0x38f/0x4e0 kernel/printk/printk.c:1996
 vprintk_default+0x31/0x50 kernel/printk/printk.c:2023
 vprintk_func+0x85/0x140 kernel/printk/printk_safe.c:386
 printk+0x69/0x91 kernel/printk/printk.c:2056
 kauditd_printk_skb kernel/audit.c:532 [inline]
 kauditd_hold_skb.cold+0x21/0x26 kernel/audit.c:565
 kauditd_send_queue+0x1b1/0x220 kernel/audit.c:728
 kauditd_thread+0x483/0x560 kernel/audit.c:854
 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: 26 Comm: kauditd 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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