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BUG: KCSAN: data-race in __lookup_mnt / __se_sys_pivot_root

write to 0xffff88814333c5d0 of 8 bytes by task 8851 on cpu 1:
 unhash_mnt fs/namespace.c:839 [inline]
 umount_mnt fs/namespace.c:854 [inline]
 __do_sys_pivot_root fs/namespace.c:3883 [inline]
 __se_sys_pivot_root+0x63d/0x1030 fs/namespace.c:3816
 __x64_sys_pivot_root+0x2d/0x40 fs/namespace.c:3816
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88814333c5d0 of 8 bytes by task 8850 on cpu 0:
 __lookup_mnt+0x89/0xf0 fs/namespace.c:630
 __follow_mount_rcu fs/namei.c:1450 [inline]
 handle_mounts fs/namei.c:1486 [inline]
 step_into+0x35c/0xee0 fs/namei.c:1800
 walk_component+0x1a1/0x360 fs/namei.c:1976
 lookup_last fs/namei.c:2425 [inline]
 path_lookupat+0x12d/0x3d0 fs/namei.c:2449
 filename_lookup+0x130/0x310 fs/namei.c:2478
 user_path_at_empty+0x3e/0x110 fs/namei.c:2801
 user_path_at include/linux/namei.h:57 [inline]
 do_mount fs/namespace.c:3328 [inline]
 __do_sys_mount fs/namespace.c:3539 [inline]
 __se_sys_mount+0x217/0x2f0 fs/namespace.c:3516
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3516
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xd0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0xffff88814333c0c0 -> 0xffff88814333c480

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8850 Comm: syz-executor.5 Not tainted 5.16.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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