syzbot

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BUG: KCSAN: data-race in __lookup_mnt / __umount_mnt

write to 0xffff888104f6aa90 of 8 bytes by task 13876 on cpu 0:
 __umount_mnt+0x4e/0x2c0 fs/namespace.c:994
 umount_mnt fs/namespace.c:1009 [inline]
 umount_tree+0x5ff/0x8a0 fs/namespace.c:1824
 do_umount fs/namespace.c:-1 [inline]
 path_umount+0x799/0x7f0 fs/namespace.c:2047
 ksys_umount fs/namespace.c:2070 [inline]
 __do_sys_umount fs/namespace.c:2075 [inline]
 __se_sys_umount fs/namespace.c:2073 [inline]
 __x64_sys_umount+0xb6/0xe0 fs/namespace.c:2073
 x64_sys_call+0x103b/0x3020 arch/x86/include/generated/asm/syscalls_64.h:167
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888104f6aa90 of 8 bytes by task 2980 on cpu 1:
 __lookup_mnt+0x84/0xf0 fs/namespace.c:796
 __follow_mount_rcu+0xbc/0x2a0 fs/namei.c:1708
 handle_mounts fs/namei.c:1740 [inline]
 step_into_slowpath+0x30c/0x4c0 fs/namei.c:2104
 step_into fs/namei.c:2152 [inline]
 walk_component fs/namei.c:2288 [inline]
 link_path_walk+0x947/0xdd0 fs/namei.c:-1
 path_lookupat+0x53/0x4c0 fs/namei.c:2812
 filename_lookup+0x18f/0x390 fs/namei.c:2842
 do_readlinkat+0x74/0x2f0 fs/stat.c:571
 __do_sys_readlink fs/stat.c:605 [inline]
 __se_sys_readlink fs/stat.c:602 [inline]
 __x64_sys_readlink+0x47/0x60 fs/stat.c:602
 x64_sys_call+0x2b51/0x3020 arch/x86/include/generated/asm/syscalls_64.h:90
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff888119982780 -> 0xffff888104f6aa80

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 2980 Comm: udevd Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
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