[moderation] [fs?] KCSAN: data-race in __dentry_kill / __dentry_kill (7)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 18f7fcd5e69a Linux 6.19-rc8
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17ef772a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8e27f4588a0f2183
dashboard link: https://syzkaller.appspot.com/bug?extid=32c4ce311ae1ea106e44
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/8157f3acb6cd/disk-18f7fcd5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0ac01f41d27b/vmlinux-18f7fcd5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f87453c1c5ae/bzImage-18f7fcd5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+32c4ce...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __dentry_kill / __dentry_kill

write to 0xffff88811a9159c0 of 4 bytes by task 3002 on cpu 1:
d_lru_del fs/dcache.c:504 [inline]
__dentry_kill+0xa8/0x460 fs/dcache.c:665
finish_dput+0x2b/0x200 fs/dcache.c:879
dput+0x52/0x60 fs/dcache.c:928
lookup_fast+0x29e/0x320 fs/namei.c:1832
walk_component fs/namei.c:2225 [inline]
lookup_last fs/namei.c:2730 [inline]
path_lookupat+0x15c/0x500 fs/namei.c:2754
filename_lookup+0x190/0x390 fs/namei.c:2783
do_readlinkat+0x7d/0x340 fs/stat.c:576
__do_sys_readlink fs/stat.c:613 [inline]
__se_sys_readlink fs/stat.c:610 [inline]
__x64_sys_readlink+0x47/0x60 fs/stat.c:610
x64_sys_call+0x2af1/0x3000 arch/x86/include/generated/asm/syscalls_64.h:90
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811a9159c0 of 4 bytes by task 3304 on cpu 0:
dentry_unlist fs/dcache.c:640 [inline]
__dentry_kill+0x25c/0x460 fs/dcache.c:684
finish_dput+0x2b/0x200 fs/dcache.c:879
dput+0x52/0x60 fs/dcache.c:928
lookup_fast+0x29e/0x320 fs/namei.c:1832
walk_component fs/namei.c:2225 [inline]
lookup_last fs/namei.c:2730 [inline]
path_lookupat+0x15c/0x500 fs/namei.c:2754
filename_lookup+0x190/0x390 fs/namei.c:2783
user_path_at+0x3e/0x130 fs/namei.c:3576
do_faccessat+0x391/0x830 fs/open.c:490
__do_sys_faccessat2 fs/open.c:544 [inline]
__se_sys_faccessat2 fs/open.c:541 [inline]
__x64_sys_faccessat2+0x51/0x60 fs/open.c:541
x64_sys_call+0x2c1a/0x3000 arch/x86/include/generated/asm/syscalls_64.h:440
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00140004 -> 0x00000004

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3304 Comm: udevd Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup