syzbot

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BUG: KCSAN: data-race in __umount_mnt / choose_mountpoint_rcu

write to 0xffff88811a499c90 of 8 bytes by task 12153 on cpu 0:
 __umount_mnt+0x4e/0x2c0 fs/namespace.c:1008
 umount_mnt fs/namespace.c:1023 [inline]
 umount_tree+0x547/0x7f0 fs/namespace.c:1818
 do_umount fs/namespace.c:-1 [inline]
 path_umount+0x7c8/0x7e0 fs/namespace.c:2041
 ksys_umount fs/namespace.c:2064 [inline]
 __do_sys_umount fs/namespace.c:2069 [inline]
 __se_sys_umount fs/namespace.c:2067 [inline]
 __x64_sys_umount+0xb6/0xe0 fs/namespace.c:2067
 x64_sys_call+0xdd2/0x3000 arch/x86/include/generated/asm/syscalls_64.h:167
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811a499c90 of 8 bytes by task 12145 on cpu 1:
 mnt_has_parent fs/mount.h:119 [inline]
 choose_mountpoint_rcu+0x2a/0x130 fs/namei.c:1385
 follow_dotdot_rcu fs/namei.c:2033 [inline]
 handle_dots+0x520/0x750 fs/namei.c:2108
 walk_component fs/namei.c:2145 [inline]
 link_path_walk+0x6d3/0x900 fs/namei.c:2519
 path_lookupat+0x63/0x2a0 fs/namei.c:2675
 filename_lookup+0x147/0x340 fs/namei.c:2705
 user_path_at+0x3e/0x130 fs/namei.c:3215
 ksys_umount fs/namespace.c:2061 [inline]
 __do_sys_umount fs/namespace.c:2069 [inline]
 __se_sys_umount fs/namespace.c:2067 [inline]
 __x64_sys_umount+0x85/0xe0 fs/namespace.c:2067
 x64_sys_call+0xdd2/0x3000 arch/x86/include/generated/asm/syscalls_64.h:167
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff88811a488a80 -> 0xffff88811a499c80

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 12145 Comm: syz.5.2878 Tainted: G        W           syzkaller #0 PREEMPT(voluntary) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
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