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BUG: KCSAN: data-race in fsnotify / fsnotify_detach_mark

write to 0xffff88812b37f5e4 of 4 bytes by task 20937 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
 inotify_release+0x21/0x30 fs/notify/inotify/inotify_user.c:273
 __fput+0x246/0x4d0 fs/file_table.c:281
 ____fput+0x11/0x20 fs/file_table.c:314
 task_work_run+0x8e/0x110 kernel/task_work.c:141
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:165 [inline]
 exit_to_user_mode_prepare+0x1b2/0x210 kernel/entry/common.c:192
 syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:267
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812b37f5e4 of 4 bytes by task 20942 on cpu 1:
 send_to_group fs/notify/fsnotify.c:297 [inline]
 fsnotify+0x713/0xe50 fs/notify/fsnotify.c:504
 __fsnotify_parent+0x3e3/0x470 fs/notify/fsnotify.c:223
 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+0x426/0x4b0 fs/read_write.c:1022
 vfs_iter_write+0x4c/0x70 fs/read_write.c:1059
 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+0x56a/0xba0 fs/read_write.c:1540
 __do_sys_sendfile64 fs/read_write.c:1595 [inline]
 __se_sys_sendfile64 fs/read_write.c:1587 [inline]
 __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1587
 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: 20942 Comm: syz-executor.2 Not tainted 5.9.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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