[moderation] [fs?] KCSAN: data-race in __d_lookup_rcu / __d_rehash (10)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cfd4039213e7 Merge tag 'io_uring-6.19-20251208' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=129faec2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c3201432211be40f
dashboard link: https://syzkaller.appspot.com/bug?extid=9cf744a6f9c8f6e72fab
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/9f556ae6e3c4/disk-cfd40392.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/efcf53c1d459/vmlinux-cfd40392.xz
kernel image: https://storage.googleapis.com/syzbot-assets/858f42961336/bzImage-cfd40392.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9cf744...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __d_lookup_rcu / __d_rehash

read to 0xffff88810051b550 of 8 bytes by task 3006 on cpu 1:
hlist_bl_unhashed include/linux/list_bl.h:54 [inline]
d_unhashed include/linux/dcache.h:366 [inline]
__d_lookup_rcu+0x21c/0x2d0 fs/dcache.c:2358
lookup_fast+0xa3/0x320 fs/namei.c:1792
walk_component fs/namei.c:2217 [inline]
link_path_walk+0x51c/0xe30 fs/namei.c:2589
path_lookupat+0x8c/0x500 fs/namei.c:2745
filename_lookup+0x147/0x340 fs/namei.c:2775
vfs_statx+0x9d/0x390 fs/stat.c:353
vfs_fstatat+0x115/0x170 fs/stat.c:375
__do_sys_newfstatat fs/stat.c:542 [inline]
__se_sys_newfstatat+0x55/0x260 fs/stat.c:536
__x64_sys_newfstatat+0x55/0x70 fs/stat.c:536
x64_sys_call+0x111f/0x3000 arch/x86/include/generated/asm/syscalls_64.h:263
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 0xffff88810051b550 of 8 bytes by task 10110 on cpu 0:
hlist_bl_add_head_rcu include/linux/rculist_bl.h:81 [inline]
__d_rehash+0x9e/0x1f0 fs/dcache.c:2534
__d_add+0x344/0x4a0 fs/dcache.c:2759
d_add+0x47/0x50 fs/dcache.c:2782
simple_lookup+0xba/0xd0 fs/libfs.c:81
lookup_one_qstr_excl+0xcb/0x250 fs/namei.c:1747
__start_dirop fs/namei.c:2866 [inline]
start_dirop fs/namei.c:2875 [inline]
filename_create+0x141/0x210 fs/namei.c:4879
do_symlinkat+0x94/0x470 fs/namei.c:5534
__do_sys_symlinkat fs/namei.c:5562 [inline]
__se_sys_symlinkat fs/namei.c:5559 [inline]
__x64_sys_symlinkat+0x5a/0x70 fs/namei.c:5559
x64_sys_call+0x2a36/0x3000 arch/x86/include/generated/asm/syscalls_64.h:267
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: 10110 Comm: syz-executor Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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