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BUG: KCSAN: data-race in __lookup_mnt / umount_tree

write to 0xffff8881627fd018 of 8 bytes by task 18483 on cpu 1:
 unhash_mnt fs/namespace.c:904 [inline]
 umount_mnt fs/namespace.c:918 [inline]
 umount_tree+0x58e/0x860 fs/namespace.c:1673
 path_umount+0x928/0x9a0 fs/namespace.c:1894
 ksys_umount fs/namespace.c:1917 [inline]
 __do_sys_umount fs/namespace.c:1922 [inline]
 __se_sys_umount fs/namespace.c:1920 [inline]
 __x64_sys_umount+0xb9/0xe0 fs/namespace.c:1920
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff8881627fd018 of 8 bytes by task 18481 on cpu 0:
 __lookup_mnt+0xa0/0xf0 fs/namespace.c:694
 __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]
 do_mount fs/namespace.c:3672 [inline]
 __do_sys_mount fs/namespace.c:3884 [inline]
 __se_sys_mount+0x24b/0x2d0 fs/namespace.c:3861
 __x64_sys_mount+0x67/0x80 fs/namespace.c:3861
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0xffff88813c0add80 -> 0xffff888105132480

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 18481 Comm: syz-executor.5 Not tainted 6.6.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/06/2023
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