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BUG: KCSAN: data-race in fsnotify / fsnotify_detach_mark

write to 0xffff88812113e47c of 4 bytes by task 30791 on cpu 1:
 fsnotify_detach_mark+0xa4/0x1d0 fs/notify/mark.c:386
 fsnotify_clear_marks_by_group+0x293/0x320 fs/notify/mark.c:757
 fsnotify_destroy_group+0x5a/0x190 fs/notify/group.c:60
 fanotify_release+0x20e/0x240 fs/notify/fanotify/fanotify_user.c:488
 __fput+0x1c3/0x4f0 fs/file_table.c:280
 ____fput+0x1b/0x30 fs/file_table.c:313
 task_work_run+0xf5/0x130 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x2ae/0x2c0 arch/x86/entry/common.c:164
 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
 do_syscall_64+0x36e/0x390 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812113e47c of 4 bytes by task 30793 on cpu 0:
 send_to_group fs/notify/fsnotify.c:209 [inline]
 fsnotify+0x3fe/0x7d0 fs/notify/fsnotify.c:372
 __fsnotify_parent+0x1d6/0x230 fs/notify/fsnotify.c:172
 fsnotify_parent include/linux/fsnotify.h:40 [inline]
 fsnotify_path include/linux/fsnotify.h:50 [inline]
 fsnotify_modify include/linux/fsnotify.h:256 [inline]
 do_iter_write fs/read_write.c:1002 [inline]
 do_iter_write+0x1e1/0x3a0 fs/read_write.c:979
 vfs_iter_write+0x56/0x80 fs/read_write.c:1039
 iter_file_splice_write+0x530/0x830 fs/splice.c:760
 do_splice_from fs/splice.c:863 [inline]
 direct_splice_actor+0x97/0xb0 fs/splice.c:1037
 splice_direct_to_actor+0x22f/0x540 fs/splice.c:992
 do_splice_direct+0x152/0x1d0 fs/splice.c:1080
 do_sendfile+0x396/0x810 fs/read_write.c:1520
 __do_sys_sendfile64 fs/read_write.c:1575 [inline]
 __se_sys_sendfile64 fs/read_write.c:1567 [inline]
 __x64_sys_sendfile64+0xb8/0x140 fs/read_write.c:1567
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 30793 Comm: syz-executor.4 Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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