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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: dd9b004b7ff3 Merge tag 'trace-v6.19-rc1' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=144ad984580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b319ff1b6a2797ca
dashboard link: https://syzkaller.appspot.com/bug?extid=8df9d8f0a279a10acd12
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [joel.g...@kernel.org ke...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9e79d07095a9/disk-dd9b004b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/17768b8878a0/vmlinux-dd9b004b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2990b6178ed7/bzImage-dd9b004b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8df9d8...@syzkaller.appspotmail.com

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

write to 0xffff888107ddf550 of 8 bytes by task 3318 on cpu 1:
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_splice_alias_ops+0xdc/0x280 fs/dcache.c:3100
proc_sys_lookup+0x1ed/0x310 fs/proc/proc_sysctl.c:544
lookup_open fs/namei.c:4413 [inline]
open_last_lookups fs/namei.c:4540 [inline]
path_openat+0xed5/0x23b0 fs/namei.c:4784
do_filp_open+0x109/0x230 fs/namei.c:4814
do_sys_openat2+0xa6/0x150 fs/open.c:1430
do_sys_open fs/open.c:1436 [inline]
__do_sys_openat fs/open.c:1452 [inline]
__se_sys_openat fs/open.c:1447 [inline]
__x64_sys_openat+0xf2/0x120 fs/open.c:1447
x64_sys_call+0x2b07/0x3000 arch/x86/include/generated/asm/syscalls_64.h:258
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888107ddf550 of 8 bytes by task 3319 on cpu 0:
hlist_bl_unhashed include/linux/list_bl.h:54 [inline]
d_unhashed include/linux/dcache.h:366 [inline]
__d_lookup+0xf8/0x340 fs/dcache.c:2445
lookup_fast+0x5e/0x320 fs/namei.c:1816
lookup_fast_for_open fs/namei.c:4477 [inline]
open_last_lookups fs/namei.c:4511 [inline]
path_openat+0x416/0x23b0 fs/namei.c:4784
do_filp_open+0x109/0x230 fs/namei.c:4814
do_sys_openat2+0xa6/0x150 fs/open.c:1430
do_sys_open fs/open.c:1436 [inline]
__do_sys_openat fs/open.c:1452 [inline]
__se_sys_openat fs/open.c:1447 [inline]
__x64_sys_openat+0xf2/0x120 fs/open.c:1447
x64_sys_call+0x2b07/0x3000 arch/x86/include/generated/asm/syscalls_64.h:258
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff8882378d4ab0 -> 0xffff888100695248

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3319 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================
chnl_net:caif_netlink_parms(): no params data found
bridge0: port 1(bridge_slave_0) entered blocking state
bridge0: port 1(bridge_slave_0) entered disabled state
bridge_slave_0: entered allmulticast mode
bridge_slave_0: entered promiscuous mode
bridge0: port 2(bridge_slave_1) entered blocking state
bridge0: port 2(bridge_slave_1) entered disabled state
bridge_slave_1: entered allmulticast mode
bridge_slave_1: entered promiscuous mode
bond0: (slave bond_slave_0): Enslaving as an active interface with an up link
bond0: (slave bond_slave_1): Enslaving as an active interface with an up link
team0: Port device team_slave_0 added
team0: Port device team_slave_1 added
batman_adv: batadv0: Adding interface: batadv_slave_0
batman_adv: batadv0: The MTU of interface batadv_slave_0 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1532 would solve the problem.
batman_adv: batadv0: Not using interface batadv_slave_0 (retrying later): interface not active
batman_adv: batadv0: Adding interface: batadv_slave_1
batman_adv: batadv0: The MTU of interface batadv_slave_1 is too small (1500) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1532 would solve the problem.
batman_adv: batadv0: Not using interface batadv_slave_1 (retrying later): interface not active
hsr_slave_0: entered promiscuous mode
hsr_slave_1: entered promiscuous mode
debugfs: 'hsr0' already exists in 'hsr'
Cannot create hsr debugfs directory
netdevsim netdevsim0 netdevsim0: renamed from eth0
netdevsim netdevsim0 netdevsim1: renamed from eth1
netdevsim netdevsim0 netdevsim2: renamed from eth2
netdevsim netdevsim0 netdevsim3: renamed from eth3
8021q: adding VLAN 0 to HW filter on device bond0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device batadv0
veth0_vlan: entered promiscuous mode
veth1_vlan: entered promiscuous mode
veth0_macvtap: entered promiscuous mode
veth1_macvtap: entered promiscuous mode
batman_adv: batadv0: Interface activated: batadv_slave_0
batman_adv: batadv0: Interface activated: batadv_slave_1


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