[moderation] [fs?] KCSAN: data-race in __d_lookup_rcu / __d_rehash (9)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 320475fbd590 Merge tag 'mtd/fixes-for-6.17-rc6' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1045f362580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6e0c213d0735f5dd
dashboard link: https://syzkaller.appspot.com/bug?extid=45f03546808c78194dc5
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/03d005b220b7/disk-320475fb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3ce8904c800d/vmlinux-320475fb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/04e70a318f85/bzImage-320475fb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+45f035...@syzkaller.appspotmail.com

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

read to 0xffff8881442ec9d0 of 8 bytes by task 32542 on cpu 1:
hlist_bl_unhashed include/linux/list_bl.h:54 [inline]
d_unhashed include/linux/dcache.h:361 [inline]
__d_lookup_rcu+0x109/0x2a0 fs/dcache.c:2309
lookup_fast+0xa3/0x320 fs/namei.c:1742
lookup_fast_for_open fs/namei.c:3745 [inline]
open_last_lookups fs/namei.c:3778 [inline]
path_openat+0x43c/0x2170 fs/namei.c:4043
do_filp_open+0x109/0x230 fs/namei.c:4073
do_sys_openat2+0xa6/0x110 fs/open.c:1435
do_sys_open fs/open.c:1450 [inline]
__do_sys_openat fs/open.c:1466 [inline]
__se_sys_openat fs/open.c:1461 [inline]
__x64_sys_openat+0xf2/0x120 fs/open.c:1461
x64_sys_call+0x2e9c/0x2ff0 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

write to 0xffff8881442ec9d0 of 8 bytes by task 32543 on cpu 0:
hlist_bl_add_head_rcu include/linux/rculist_bl.h:81 [inline]
__d_rehash+0x9e/0x1f0 fs/dcache.c:2489
d_rehash+0x26/0x40 fs/dcache.c:2503
shmem_whiteout mm/shmem.c:4087 [inline]
shmem_rename2+0x1e4/0x290 mm/shmem.c:4117
vfs_rename+0x7f3/0xa40 fs/namei.c:5129
do_renameat2+0x557/0xa10 fs/namei.c:5278
__do_sys_renameat2 fs/namei.c:5312 [inline]
__se_sys_renameat2 fs/namei.c:5309 [inline]
__x64_sys_renameat2+0x7e/0x90 fs/namei.c:5309
x64_sys_call+0x3f9/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:317
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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 32543 Comm: syz.6.6055 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================


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