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BUG: KCSAN: data-race in __d_instantiate / lookup_fast

write to 0xffff88812f624840 of 4 bytes by task 20996 on cpu 1:
 fsnotify_update_flags include/linux/fsnotify_backend.h:460 [inline]
 __d_instantiate+0x2c5/0x3c0 fs/dcache.c:1985
 d_instantiate_new+0x58/0x110 fs/dcache.c:2029
 ext4_mkdir+0x5fa/0x760 fs/ext4/namei.c:2955
 vfs_mkdir+0x2a4/0x370 fs/namei.c:3823
 do_mkdirat+0x11d/0x200 fs/namei.c:3848
 __do_sys_mkdir fs/namei.c:3866 [inline]
 __se_sys_mkdir fs/namei.c:3864 [inline]
 __x64_sys_mkdir+0x32/0x40 fs/namei.c:3864
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88812f624840 of 4 bytes by task 20977 on cpu 0:
 d_revalidate fs/namei.c:842 [inline]
 lookup_fast+0x15f/0x350 fs/namei.c:1595
 walk_component+0x5c/0x350 fs/namei.c:1955
 lookup_last fs/namei.c:2414 [inline]
 path_lookupat+0x12d/0x3d0 fs/namei.c:2438
 filename_lookup+0x118/0x3b0 fs/namei.c:2467
 user_path_at_empty+0x3b/0x50 fs/namei.c:2747
 user_path_at include/linux/namei.h:57 [inline]
 path_setxattr+0x4b/0x180 fs/xattr.c:590
 __do_sys_setxattr fs/xattr.c:611 [inline]
 __se_sys_setxattr fs/xattr.c:607 [inline]
 __x64_sys_setxattr+0x69/0x80 fs/xattr.c:607
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000000 -> 0x00280000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 20977 Comm: syz-executor.1 Not tainted 5.14.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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