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BUG: KCSAN: data-race in __lookup_mnt / __se_sys_pivot_root

write to 0xffff88813548d298 of 8 bytes by task 10350 on cpu 0:
 unhash_mnt fs/namespace.c:881 [inline]
 umount_mnt fs/namespace.c:895 [inline]
 __do_sys_pivot_root fs/namespace.c:3935 [inline]
 __se_sys_pivot_root+0x66b/0x1060 fs/namespace.c:3868
 __x64_sys_pivot_root+0x31/0x40 fs/namespace.c:3868
 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 0xffff88813548d298 of 8 bytes by task 10349 on cpu 1:
 __lookup_mnt+0xa0/0xf0 fs/namespace.c:671
 __follow_mount_rcu fs/namei.c:1504 [inline]
 handle_mounts fs/namei.c:1534 [inline]
 step_into+0x430/0x800 fs/namei.c:1836
 walk_component+0x164/0x230 fs/namei.c:2004
 lookup_last fs/namei.c:2455 [inline]
 path_lookupat+0x10a/0x2a0 fs/namei.c:2479
 filename_lookup+0x126/0x300 fs/namei.c:2508
 user_path_at_empty+0x42/0x110 fs/namei.c:2907
 user_path_at include/linux/namei.h:57 [inline]
 __do_sys_pivot_root fs/namespace.c:3884 [inline]
 __se_sys_pivot_root+0x113/0x1060 fs/namespace.c:3868
 __x64_sys_pivot_root+0x31/0x40 fs/namespace.c:3868
 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: 0xffff88816085ce40 -> 0xffff888100403a80

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 10349 Comm: syz-executor.3 Not tainted 6.4.0-rc4-syzkaller-00031-g8b817fded42d #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/25/2023
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