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BUG: KCSAN: data-race in enqueue_timer / timer_reduce

write to 0xffff8880a5df6918 of 8 bytes by task 7887 on cpu 1:
 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:1644
 queue_delayed_work_on+0xf3/0x110 kernel/workqueue.c:1669
 queue_delayed_work include/linux/workqueue.h:509 [inline]
 fsnotify_put_mark+0x29c/0x3f0 fs/notify/mark.c:276
 __do_sys_inotify_rm_watch fs/notify/inotify/inotify_user.c:790 [inline]
 __se_sys_inotify_rm_watch fs/notify/inotify/inotify_user.c:762 [inline]
 __x64_sys_inotify_rm_watch+0xd7/0x130 fs/notify/inotify/inotify_user.c:762
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880a5df6918 of 8 bytes by task 13546 on cpu 0:
 __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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 13546 Comm: syz-executor.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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