syzbot

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BUG: KCSAN: data-race in choose_mountpoint_rcu / mnt_change_mountpoint

write to 0xffff88811da2ed90 of 8 bytes by task 7838 on cpu 1:
 mnt_set_mountpoint fs/namespace.c:1025 [inline]
 attach_mnt fs/namespace.c:1059 [inline]
 mnt_change_mountpoint+0x1ab/0x490 fs/namespace.c:1071
 reparent fs/pnode.c:641 [inline]
 propagate_umount+0xd24/0xf30 fs/pnode.c:682
 umount_tree+0x2f8/0x800 fs/namespace.c:1790
 do_umount fs/namespace.c:-1 [inline]
 path_umount+0x7c0/0x810 fs/namespace.c:2038
 ksys_umount fs/namespace.c:2061 [inline]
 __do_sys_umount fs/namespace.c:2066 [inline]
 __se_sys_umount fs/namespace.c:2064 [inline]
 __x64_sys_umount+0xb6/0xe0 fs/namespace.c:2064
 x64_sys_call+0xd6a/0x3000 arch/x86/include/generated/asm/syscalls_64.h:167
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811da2ed90 of 8 bytes by task 7837 on cpu 0:
 mnt_has_parent fs/mount.h:120 [inline]
 choose_mountpoint_rcu+0x2a/0x130 fs/namei.c:1425
 follow_dotdot_rcu fs/namei.c:2103 [inline]
 handle_dots+0x63d/0x8a0 fs/namei.c:2178
 walk_component fs/namei.c:2215 [inline]
 link_path_walk+0x8bb/0xe30 fs/namei.c:2589
 path_lookupat+0x8c/0x500 fs/namei.c:2745
 filename_lookup+0x147/0x340 fs/namei.c:2775
 user_path_at+0x3e/0x130 fs/namei.c:3567
 ksys_umount fs/namespace.c:2058 [inline]
 __do_sys_umount fs/namespace.c:2066 [inline]
 __se_sys_umount fs/namespace.c:2064 [inline]
 __x64_sys_umount+0x85/0xe0 fs/namespace.c:2064
 x64_sys_call+0xd6a/0x3000 arch/x86/include/generated/asm/syscalls_64.h:167
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff888104640300 -> 0xffff888104641380

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 7837 Comm: syz.5.1204 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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