[moderation] [fs?] KCSAN: data-race in __d_lookup / shrink_dentry_list

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0031c06807cf Merge tag 'cgroup-for-7.0-rc2-fixes' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12c9fbe6580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6b32b22d8934c136
dashboard link: https://syzkaller.appspot.com/bug?extid=3c88ac1670cd4b50088c
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
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/4e24462b7c3a/disk-0031c068.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/de3ed600677d/vmlinux-0031c068.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b339fd8fe415/bzImage-0031c068.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3c88ac...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __d_lookup / shrink_dentry_list

read-write to 0xffff88811af743c0 of 4 bytes by task 17691 on cpu 1:
d_shrink_del fs/dcache.c:516 [inline]
shrink_dentry_list+0x22d/0x3c0 fs/dcache.c:1166
shrink_dcache_sb+0x15d/0x290 fs/dcache.c:1295
reconfigure_super+0x142/0x590 fs/super.c:1058
do_remount fs/namespace.c:3391 [inline]
path_mount+0xaf7/0xbc0 fs/namespace.c:4151
do_mount fs/namespace.c:4172 [inline]
__do_sys_mount fs/namespace.c:4361 [inline]
__se_sys_mount+0x28c/0x2e0 fs/namespace.c:4338
__x64_sys_mount+0x67/0x80 fs/namespace.c:4338
x64_sys_call+0x2d61/0x3020 arch/x86/include/generated/asm/syscalls_64.h:166
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811af743c0 of 4 bytes by task 16537 on cpu 0:
d_same_name fs/dcache.c:2220 [inline]
__d_lookup+0x118/0x340 fs/dcache.c:2458
lookup_fast+0x5e/0x320 fs/namei.c:1874
walk_component fs/namei.c:2275 [inline]
link_path_walk+0x51c/0xe30 fs/namei.c:2647
path_parentat fs/namei.c:2851 [inline]
__filename_parentat+0x1a4/0x450 fs/namei.c:2875
filename_parentat fs/namei.c:2893 [inline]
filename_unlinkat+0x99/0x410 fs/namei.c:5509
__do_sys_unlink fs/namei.c:5575 [inline]
__se_sys_unlink+0x2b/0xe0 fs/namei.c:5572
__x64_sys_unlink+0x1f/0x30 fs/namei.c:5572
x64_sys_call+0x2eb6/0x3020 arch/x86/include/generated/asm/syscalls_64.h:88
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00140444 -> 0x00100044

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 16537 Comm: syz-executor Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================


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