[moderation] [fs?] KCSAN: data-race in lookup_fast / shrink_dentry_list (14)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0e35b9b6ec0f Merge tag 'mm-hotfixes-stable-2026-07-06-17-4..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14289b1e580000
kernel config: https://syzkaller.appspot.com/x/.config?x=84b3039e8461eef5
dashboard link: https://syzkaller.appspot.com/bug?extid=520e215f5f5030595cd3
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
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/50ec388edb4b/disk-0e35b9b6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d5fde077ecdc/vmlinux-0e35b9b6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e0545f5d0fb1/bzImage-0e35b9b6.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+520e21...@syzkaller.appspotmail.com

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

read-write to 0xffff8881078e2540 of 4 bytes by task 4328 on cpu 1:
d_shrink_del fs/dcache.c:527 [inline]
shrink_dentry_list+0x108/0x1d0 fs/dcache.c:1286
shrink_dcache_sb+0x161/0x290 fs/dcache.c:1413
reconfigure_super+0x472/0x590 fs/super.c:998
do_remount fs/namespace.c:3407 [inline]
path_mount+0xaba/0xb90 fs/namespace.c:4153
do_mount fs/namespace.c:4174 [inline]
__do_sys_mount fs/namespace.c:4390 [inline]
__se_sys_mount+0x28c/0x2e0 fs/namespace.c:4367
__x64_sys_mount+0x67/0x80 fs/namespace.c:4367
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+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881078e2540 of 4 bytes by task 3289 on cpu 0:
d_revalidate fs/namei.c:1034 [inline]
lookup_fast+0x72/0x320 fs/namei.c:1881
lookup_fast_for_open fs/namei.c:4545 [inline]
open_last_lookups fs/namei.c:4579 [inline]
path_openat+0x423/0x2000 fs/namei.c:4860
do_file_open+0x16c/0x290 fs/namei.c:4892
do_sys_openat2+0xa0/0x130 fs/open.c:1368
do_sys_open fs/open.c:1374 [inline]
__do_sys_openat fs/open.c:1390 [inline]
__se_sys_openat fs/open.c:1385 [inline]
__x64_sys_openat+0xf2/0x120 fs/open.c:1385
x64_sys_call+0x1e39/0x3020 arch/x86/include/generated/asm/syscalls_64.h:258
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: 0x00340444 -> 0x00300044

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3289 Comm: udevd Not tainted syzkaller #0 PREEMPT(lazy)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
==================================================================


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