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BUG: KCSAN: data-race in fsnotify / fsnotify_detach_mark

write to 0xffff88811f8c086c of 4 bytes by task 11055 on cpu 0:
 fsnotify_detach_mark+0x80/0x120 fs/notify/mark.c:390
 fsnotify_clear_marks_by_group+0x298/0x3e0 fs/notify/mark.c:761
 fsnotify_destroy_group+0x51/0x170 fs/notify/group.c:61
 fanotify_release+0x2c5/0x2e0 fs/notify/fanotify/fanotify_user.c:557
 __fput+0x1df/0x460 fs/file_table.c:281
 ____fput+0x11/0x20 fs/file_table.c:314
 task_work_run+0x8e/0x110 kernel/task_work.c:123
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop arch/x86/entry/common.c:216 [inline]
 __prepare_exit_to_usermode+0x1c8/0x230 arch/x86/entry/common.c:246
 __syscall_return_slowpath arch/x86/entry/common.c:329 [inline]
 do_syscall_64+0xb9/0x120 arch/x86/entry/common.c:368
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88811f8c086c of 4 bytes by task 11057 on cpu 1:
 send_to_group fs/notify/fsnotify.c:202 [inline]
 fsnotify+0x513/0x9e0 fs/notify/fsnotify.c:366
 fsnotify_parent+0x128/0x180 fs/notify/fsnotify.c:169
 fsnotify_file include/linux/fsnotify.h:74 [inline]
 fsnotify_modify include/linux/fsnotify.h:257 [inline]
 do_iter_write+0x1af/0x470 fs/read_write.c:1003
 vfs_iter_write+0x4c/0x70 fs/read_write.c:1040
 iter_file_splice_write+0x41a/0x770 fs/splice.c:750
 do_splice_from fs/splice.c:846 [inline]
 direct_splice_actor+0x95/0x160 fs/splice.c:1016
 splice_direct_to_actor+0x365/0x660 fs/splice.c:971
 do_splice_direct+0xf2/0x170 fs/splice.c:1059
 do_sendfile+0x562/0xb10 fs/read_write.c:1521
 __do_sys_sendfile64 fs/read_write.c:1576 [inline]
 __se_sys_sendfile64 fs/read_write.c:1568 [inline]
 __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1568
 do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 11057 Comm: syz-executor.0 Not tainted 5.8.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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