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BUG: KCSAN: data-race in __fsnotify_update_child_dentry_flags / file_remove_privs

write to 0xffff8881415216c0 of 4 bytes by task 2399 on cpu 0:
 __fsnotify_update_child_dentry_flags+0x147/0x270 fs/notify/fsnotify.c:134
 fsnotify_recalc_mask+0x1e2/0x200 fs/notify/mark.c:150
 fsnotify_add_mark_locked+0x80b/0xa10 fs/notify/mark.c:665
 fsnotify_add_inode_mark_locked include/linux/fsnotify_backend.h:548 [inline]
 inotify_new_watch fs/notify/inotify/inotify_user.c:596 [inline]
 inotify_update_watch fs/notify/inotify/inotify_user.c:623 [inline]
 __do_sys_inotify_add_watch fs/notify/inotify/inotify_user.c:761 [inline]
 __se_sys_inotify_add_watch+0x537/0x670 fs/notify/inotify/inotify_user.c:704
 __x64_sys_inotify_add_watch+0x3f/0x50 fs/notify/inotify/inotify_user.c:704
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881415216c0 of 4 bytes by task 2392 on cpu 1:
 d_real include/linux/dcache.h:586 [inline]
 file_dentry include/linux/fs.h:1311 [inline]
 file_remove_privs+0x39/0x3a0 fs/inode.c:1927
 file_modified+0x16/0x80 fs/inode.c:2010
 ext4_write_checks fs/ext4/file.c:247 [inline]
 ext4_buffered_write_iter+0x1f9/0x3f0 fs/ext4/file.c:264
 ext4_file_write_iter+0x2e7/0x11d0 fs/ext4/file.c:519
 call_write_iter include/linux/fs.h:2116 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:740
 do_iter_write+0x112/0x4c0 fs/read_write.c:866
 vfs_iter_write+0x4c/0x70 fs/read_write.c:907
 iter_file_splice_write+0x40a/0x750 fs/splice.c:689
 do_splice_from fs/splice.c:767 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:936
 splice_direct_to_actor+0x345/0x650 fs/splice.c:891
 do_splice_direct+0xf5/0x170 fs/splice.c:979
 do_sendfile+0x773/0xda0 fs/read_write.c:1260
 __do_sys_sendfile64 fs/read_write.c:1319 [inline]
 __se_sys_sendfile64 fs/read_write.c:1311 [inline]
 __x64_sys_sendfile64+0xa9/0x130 fs/read_write.c:1311
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 2392 Comm: syz-executor.3 Not tainted 5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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