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BUG: KCSAN: data-race in __d_instantiate / step_into

read-write to 0xffff88814306d000 of 4 bytes by task 6358 on cpu 0:
 __d_instantiate+0x2cd/0x3c0 fs/dcache.c:1855
 d_instantiate_new+0x5c/0xf0 fs/dcache.c:1899
 ext4_mkdir+0x5e5/0x740 fs/ext4/namei.c:3048
 vfs_mkdir+0x1ef/0x2f0 fs/namei.c:4122
 do_mkdirat+0x12f/0x2a0 fs/namei.c:4145
 __do_sys_mkdirat fs/namei.c:4160 [inline]
 __se_sys_mkdirat fs/namei.c:4158 [inline]
 __x64_sys_mkdirat+0x50/0x60 fs/namei.c:4158
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff88814306d000 of 4 bytes by task 6359 on cpu 1:
 __d_entry_type include/linux/dcache.h:391 [inline]
 d_is_symlink include/linux/dcache.h:421 [inline]
 step_into+0x12f/0x800 fs/namei.c:1844
 walk_component+0x164/0x230 fs/namei.c:2007
 lookup_last fs/namei.c:2458 [inline]
 path_lookupat+0x10a/0x2a0 fs/namei.c:2482
 filename_lookup+0x126/0x300 fs/namei.c:2511
 user_path_at_empty+0x42/0x120 fs/namei.c:2920
 user_path_at include/linux/namei.h:57 [inline]
 do_mount fs/namespace.c:3689 [inline]
 __do_sys_mount fs/namespace.c:3898 [inline]
 __se_sys_mount+0x24b/0x2d0 fs/namespace.c:3875
 __x64_sys_mount+0x67/0x80 fs/namespace.c:3875
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0x00000000 -> 0x00280000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 6359 Comm: syz-executor.2 Not tainted 6.8.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
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