BUG: KCSAN: data-race in __lookup_mnt / umount_tree

write to 0xffff888187c8d510 of 8 bytes by task 26251 on cpu 0:
 unhash_mnt fs/namespace.c:905 [inline]
 umount_mnt fs/namespace.c:920 [inline]
 umount_tree+0x574/0x860 fs/namespace.c:1675
 path_umount+0x928/0x9a0 fs/namespace.c:1896
 ksys_umount fs/namespace.c:1919 [inline]
 __do_sys_umount fs/namespace.c:1924 [inline]
 __se_sys_umount fs/namespace.c:1922 [inline]
 __x64_sys_umount+0xb9/0xe0 fs/namespace.c:1922
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff888187c8d510 of 8 bytes by task 26253 on cpu 1:
 __lookup_mnt+0x83/0xf0 fs/namespace.c:696
 __follow_mount_rcu fs/namei.c:1508 [inline]
 handle_mounts fs/namei.c:1538 [inline]
 step_into+0x430/0x800 fs/namei.c:1840
 walk_component+0x164/0x230 fs/namei.c:2008
 lookup_last fs/namei.c:2459 [inline]
 path_lookupat+0x10a/0x2a0 fs/namei.c:2483
 filename_lookup+0x126/0x300 fs/namei.c:2512
 user_path_at_empty+0x42/0x110 fs/namei.c:2911
 user_path_at include/linux/namei.h:57 [inline]
 ksys_umount fs/namespace.c:1916 [inline]
 __do_sys_umount fs/namespace.c:1924 [inline]
 __se_sys_umount fs/namespace.c:1922 [inline]
 __x64_sys_umount+0x88/0xe0 fs/namespace.c:1922
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0xffff88813cb2cb40 -> 0xffff888187c8d500

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 26253 Comm: syz-executor.3 Not tainted 6.7.0-rc1-syzkaller-00019-gc42d9eeef8e5 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
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