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BUG: KCSAN: data-race in __d_instantiate / step_into

read-write to 0xffff888108142600 of 4 bytes by task 30362 on cpu 1:
 __d_instantiate+0x2cd/0x3c0 fs/dcache.c:1855
 d_instantiate_new+0x5c/0xf0 fs/dcache.c:1899
 ext4_mkdir+0x5e6/0x740 fs/ext4/namei.c:3047
 vfs_mkdir+0x1f7/0x300 fs/namei.c:4123
 do_mkdirat+0x12f/0x2a0 fs/namei.c:4146
 __do_sys_mkdirat fs/namei.c:4161 [inline]
 __se_sys_mkdirat fs/namei.c:4159 [inline]
 __x64_sys_mkdirat+0x50/0x60 fs/namei.c:4159
 do_syscall_64+0xd3/0x1d0
 entry_SYSCALL_64_after_hwframe+0x72/0x7a

read to 0xffff888108142600 of 4 bytes by task 30364 on cpu 0:
 __follow_mount_rcu fs/namei.c:1485 [inline]
 handle_mounts fs/namei.c:1536 [inline]
 step_into+0xe7/0x810 fs/namei.c:1842
 walk_component+0x169/0x230 fs/namei.c:2010
 lookup_last fs/namei.c:2461 [inline]
 path_lookupat+0x10a/0x2b0 fs/namei.c:2485
 filename_lookup+0x127/0x300 fs/namei.c:2514
 user_path_at_empty+0x42/0x120 fs/namei.c:2921
 user_path_at include/linux/namei.h:57 [inline]
 __do_sys_chdir fs/open.c:558 [inline]
 __se_sys_chdir+0x4f/0x150 fs/open.c:552
 __x64_sys_chdir+0x1f/0x30 fs/open.c:552
 do_syscall_64+0xd3/0x1d0
 entry_SYSCALL_64_after_hwframe+0x72/0x7a

value changed: 0x00000000 -> 0x00280000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 30364 Comm: syz-executor.3 Tainted: G        W          6.9.0-rc2-syzkaller-00080-gc85af715cac0 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
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