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BUG: KCSAN: data-race in __d_instantiate / lookup_fast

read-write to 0xffff8881380ef900 of 4 bytes by task 5684 on cpu 1:
 __d_instantiate+0x2cd/0x3b0 fs/dcache.c:2011
 d_instantiate_new+0x58/0xe0 fs/dcache.c:2055
 ext4_mkdir+0x5ff/0x760 fs/ext4/namei.c:3013
 vfs_mkdir+0x216/0x320 fs/namei.c:3954
 do_mkdirat+0x105/0x280 fs/namei.c:3980
 __do_sys_mkdir fs/namei.c:4000 [inline]
 __se_sys_mkdir fs/namei.c:3998 [inline]
 __x64_sys_mkdir+0x40/0x50 fs/namei.c:3998
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff8881380ef900 of 4 bytes by task 5685 on cpu 0:
 d_revalidate fs/namei.c:855 [inline]
 lookup_fast+0xca/0x270 fs/namei.c:1634
 walk_component+0x3f/0x230 fs/namei.c:1989
 lookup_last fs/namei.c:2450 [inline]
 path_lookupat+0x11d/0x2b0 fs/namei.c:2474
 filename_lookup+0x133/0x310 fs/namei.c:2503
 user_path_at_empty+0x3e/0x110 fs/namei.c:2876
 user_path_at include/linux/namei.h:57 [inline]
 do_mount fs/namespace.c:3380 [inline]
 __do_sys_mount fs/namespace.c:3591 [inline]
 __se_sys_mount+0x24d/0x2d0 fs/namespace.c:3568
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3568
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x00080000 -> 0x00280040

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 5685 Comm: syz-executor.3 Not tainted 5.19.0-syzkaller-10895-g6614a3c3164a-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
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