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BUG: KCSAN: data-race in fsnotify / fsnotify_detach_mark

write to 0xffff8881208236bc of 4 bytes by task 9594 on cpu 1:
 fsnotify_detach_mark+0xaa/0x1f0 fs/notify/mark.c:386
 fsnotify_clear_marks_by_group+0x299/0x320 fs/notify/mark.c:757
 fsnotify_destroy_group+0x66/0x190 fs/notify/group.c:60
 fanotify_release+0x212/0x240 fs/notify/fanotify/fanotify_user.c:488
 __fput+0x1e1/0x520 fs/file_table.c:280
 ____fput+0x1f/0x30 fs/file_table.c:313
 task_work_run+0xf6/0x130 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x2b4/0x2c0 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+0x384/0x3a0 arch/x86/entry/common.c:304
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881208236bc of 4 bytes by task 9597 on cpu 0:
 send_to_group fs/notify/fsnotify.c:209 [inline]
 fsnotify+0x3f7/0x7d0 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+0x1e7/0x3c0 fs/read_write.c:979
 vfs_iter_write+0x5c/0x80 fs/read_write.c:1039
 iter_file_splice_write+0x536/0x850 fs/splice.c:760
 do_splice_from fs/splice.c:863 [inline]
 direct_splice_actor+0xa0/0xc0 fs/splice.c:1037
 splice_direct_to_actor+0x22b/0x540 fs/splice.c:992
 do_splice_direct+0x161/0x1e0 fs/splice.c:1080
 do_sendfile+0x384/0x7f0 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+0xbe/0x140 fs/read_write.c:1567
 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: 9597 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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