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BUG: KCSAN: data-race in __se_sys_pivot_root / choose_mountpoint_rcu

write to 0xffff888130bc2150 of 8 bytes by task 1649 on cpu 0:
 unhash_mnt fs/namespace.c:903 [inline]
 umount_mnt fs/namespace.c:918 [inline]
 __do_sys_pivot_root fs/namespace.c:4233 [inline]
 __se_sys_pivot_root+0x642/0x1090 fs/namespace.c:4166
 __x64_sys_pivot_root+0x31/0x40 fs/namespace.c:4166
 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 0xffff888130bc2150 of 8 bytes by task 1648 on cpu 1:
 mnt_has_parent fs/mount.h:91 [inline]
 choose_mountpoint_rcu+0x2b/0x130 fs/namei.c:1299
 follow_dotdot_rcu fs/namei.c:1883 [inline]
 handle_dots+0x543/0x750 fs/namei.c:1958
 walk_component fs/namei.c:1995 [inline]
 link_path_walk+0x5e3/0x7e0 fs/namei.c:2328
 path_lookupat+0x72/0x2a0 fs/namei.c:2481
 filename_lookup+0x126/0x300 fs/namei.c:2511
 user_path_at_empty+0x42/0x110 fs/namei.c:2910
 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: 0xffff888130bc2000 -> 0xffff88812fd1eb40

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1648 Comm: syz-executor.1 Tainted: G        W          6.5.0-syzkaller-01810-gf97e18a3f2fb #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023
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