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BUG: KCSAN: data-race in fsnotify / fsnotify_detach_mark

write to 0xffff88802dd1e47c of 4 bytes by task 17231 on cpu 0:
 fsnotify_detach_mark+0x80/0x120 fs/notify/mark.c:390
 fsnotify_clear_marks_by_group+0x29b/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:623
 __fput+0x24b/0x4e0 fs/file_table.c:280
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0x8e/0x110 kernel/task_work.c:140
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x16b/0x1a0 kernel/entry/common.c:201
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88802dd1e47c of 4 bytes by task 17234 on cpu 1:
 send_to_group fs/notify/fsnotify.c:335 [inline]
 fsnotify+0x7c3/0x1190 fs/notify/fsnotify.c:541
 __fsnotify_parent+0x2f3/0x430 fs/notify/fsnotify.c:232
 fsnotify_parent include/linux/fsnotify.h:68 [inline]
 fsnotify_file include/linux/fsnotify.h:90 [inline]
 fsnotify_modify include/linux/fsnotify.h:255 [inline]
 do_iter_write+0x432/0x4b0 fs/read_write.c:870
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x42a/0x780 fs/splice.c:686
 do_splice_from fs/splice.c:764 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:933
 splice_direct_to_actor+0x345/0x650 fs/splice.c:888
 do_splice_direct+0xf5/0x170 fs/splice.c:976
 do_sendfile+0x5db/0xca0 fs/read_write.c:1257
 __do_sys_sendfile64 fs/read_write.c:1312 [inline]
 __se_sys_sendfile64 fs/read_write.c:1304 [inline]
 __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1304
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 17234 Comm: syz-executor.5 Not tainted 5.11.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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