[moderation] [fs?] KCSAN: data-race in __follow_mount_rcu / d_set_mounted

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d61f1cc5db79 Merge tag 'x86_cpu_for_6.19-rc1' of git://git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15a3f484580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7ca02f11a9b5ae98
dashboard link: https://syzkaller.appspot.com/bug?extid=ef7e2e63add8cfdc684f
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [bra...@kernel.org ja...@suse.cz linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/21bb911c887b/disk-d61f1cc5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e3c2031cd2c9/vmlinux-d61f1cc5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b160f4313baa/bzImage-d61f1cc5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ef7e2e...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __follow_mount_rcu / d_set_mounted

read to 0xffff88810053a0c0 of 4 bytes by task 3329 on cpu 1:
__follow_mount_rcu+0x19a/0x2f0 fs/namei.c:1651
handle_mounts fs/namei.c:1677 [inline]
step_into_slowpath+0x2f3/0x480 fs/namei.c:2043
step_into fs/namei.c:2091 [inline]
walk_component fs/namei.c:2227 [inline]
link_path_walk+0x974/0xe30 fs/namei.c:2589
path_parentat fs/namei.c:2793 [inline]
__filename_parentat+0x15c/0x3f0 fs/namei.c:2817
filename_parentat fs/namei.c:2835 [inline]
do_unlinkat+0x94/0x4b0 fs/namei.c:5408
__do_sys_unlink fs/namei.c:5474 [inline]
__se_sys_unlink fs/namei.c:5472 [inline]
__x64_sys_unlink+0x2e/0x40 fs/namei.c:5472
x64_sys_call+0x2f48/0x3000 arch/x86/include/generated/asm/syscalls_64.h:88
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

write to 0xffff88810053a0c0 of 4 bytes by task 4080 on cpu 0:
d_set_mounted+0xff/0x160 fs/dcache.c:1454
get_mountpoint+0x197/0x370 fs/namespace.c:903
attach_recursive_mnt+0x11a/0x14c0 fs/namespace.c:2579
do_move_mount+0x42e/0x470 fs/namespace.c:3574
do_move_mount_old+0x9d/0xd0 fs/namespace.c:3589
path_mount+0x550/0xb80 fs/namespace.c:4020
do_mount fs/namespace.c:4035 [inline]
__do_sys_mount fs/namespace.c:4224 [inline]
__se_sys_mount+0x28c/0x2e0 fs/namespace.c:4201
__x64_sys_mount+0x67/0x80 fs/namespace.c:4201
x64_sys_call+0x2cca/0x3000 arch/x86/include/generated/asm/syscalls_64.h:166
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 4080 Comm: syz.7.161 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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