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BUG: KCSAN: data-race in __d_instantiate / lookup_fast

write to 0xffff88810c3e0c00 of 4 bytes by task 30658 on cpu 1:
 fsnotify_update_flags include/linux/fsnotify_backend.h:463 [inline]
 __d_instantiate+0x2ca/0x3a0 fs/dcache.c:1957
 d_instantiate+0x55/0x80 fs/dcache.c:1982
 shmem_mknod+0x12f/0x170 mm/shmem.c:2939
 shmem_mkdir+0x26/0x50 mm/shmem.c:2976
 vfs_mkdir+0x288/0x350 fs/namei.c:3652
 do_mkdirat+0x132/0x220 fs/namei.c:3675
 __do_sys_mkdir fs/namei.c:3691 [inline]
 __se_sys_mkdir fs/namei.c:3689 [inline]
 __x64_sys_mkdir+0x32/0x40 fs/namei.c:3689
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88810c3e0c00 of 4 bytes by task 30664 on cpu 0:
 d_revalidate fs/namei.c:767 [inline]
 lookup_fast+0x15f/0x370 fs/namei.c:1493
 walk_component+0x5c/0x350 fs/namei.c:1857
 lookup_last fs/namei.c:2312 [inline]
 path_lookupat+0x12d/0x560 fs/namei.c:2336
 filename_lookup+0xf2/0x380 fs/namei.c:2369
 user_path_at_empty+0x3b/0x50 fs/namei.c:2649
 user_path_at include/linux/namei.h:59 [inline]
 vfs_statx+0x98/0x290 fs/stat.c:185
 vfs_fstatat fs/stat.c:207 [inline]
 vfs_stat include/linux/fs.h:3118 [inline]
 __do_sys_newstat fs/stat.c:349 [inline]
 __se_sys_newstat+0x46/0x250 fs/stat.c:345
 __x64_sys_newstat+0x2d/0x40 fs/stat.c:345
 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: 0 PID: 30664 Comm: systemd-udevd Not tainted 5.11.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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