[moderation] [fs?] KCSAN: data-race in lookup_fast / shrink_dentry_list (12)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6146a0f1dfae Linux 6.18-rc4
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15cba012580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d2e0bc0ae94545f7
dashboard link: https://syzkaller.appspot.com/bug?extid=ade48026cfd8dbd56f15
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/770acc133e5b/disk-6146a0f1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a16ceb1f509c/vmlinux-6146a0f1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/fa7d92bfe282/bzImage-6146a0f1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ade480...@syzkaller.appspotmail.com

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

read-write to 0xffff8881056e6240 of 4 bytes by task 12359 on cpu 0:
d_shrink_del fs/dcache.c:515 [inline]
shrink_dentry_list+0x22d/0x3d0 fs/dcache.c:1133
shrink_dcache_sb+0x14f/0x280 fs/dcache.c:1261
reconfigure_super+0x46a/0x580 fs/super.c:1054
do_remount fs/namespace.c:3279 [inline]
path_mount+0xad2/0xb70 fs/namespace.c:4029
do_mount fs/namespace.c:4050 [inline]
__do_sys_mount fs/namespace.c:4238 [inline]
__se_sys_mount+0x28c/0x2e0 fs/namespace.c:4215
__x64_sys_mount+0x67/0x80 fs/namespace.c:4215
x64_sys_call+0x2b51/0x3000 arch/x86/include/generated/asm/syscalls_64.h:166
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 0xffff8881056e6240 of 4 bytes by task 11791 on cpu 1:
d_revalidate fs/namei.c:928 [inline]
lookup_fast+0x72/0x320 fs/namei.c:1777
lookup_fast_for_open fs/namei.c:3833 [inline]
open_last_lookups fs/namei.c:3866 [inline]
path_openat+0x43c/0x2170 fs/namei.c:4131
do_filp_open+0x109/0x230 fs/namei.c:4161
do_sys_openat2+0xa6/0x110 fs/open.c:1437
do_sys_open fs/open.c:1452 [inline]
__do_sys_openat fs/open.c:1468 [inline]
__se_sys_openat fs/open.c:1463 [inline]
__x64_sys_openat+0xf2/0x120 fs/open.c:1463
x64_sys_call+0x2eab/0x3000 arch/x86/include/generated/asm/syscalls_64.h:258
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: 0x00240444 -> 0x00200044

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 11791 Comm: syz-executor 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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