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BUG: KCSAN: data-race in __lookup_mnt / umount_tree

write to 0xffff888104103218 of 8 bytes by task 4547 on cpu 1:
 unhash_mnt fs/namespace.c:892 [inline]
 umount_mnt fs/namespace.c:906 [inline]
 umount_tree+0x63f/0x910 fs/namespace.c:1673
 path_umount+0x98a/0xa10 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
 x64_sys_call+0x3af/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:167
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888104103218 of 8 bytes by task 4548 on cpu 0:
 __lookup_mnt+0xa0/0xf0 fs/namespace.c:701
 __follow_mount_rcu fs/namei.c:1506 [inline]
 handle_mounts fs/namei.c:1536 [inline]
 step_into+0x434/0x810 fs/namei.c:1842
 walk_component fs/namei.c:2010 [inline]
 link_path_walk+0x49d/0x810 fs/namei.c:2331
 path_lookupat+0x72/0x2b0 fs/namei.c:2492
 filename_lookup+0x127/0x300 fs/namei.c:2522
 user_path_at_empty+0x42/0x120 fs/namei.c:2929
 user_path_at include/linux/namei.h:58 [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
 x64_sys_call+0x3af/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:167
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff888108806b40 -> 0xffff888108806d80

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 4548 Comm: syz.4.338 Not tainted 6.10.0-rc6-syzkaller-00069-g795c58e4c7fc #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
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