[moderation] [fs?] KCSAN: data-race in __d_lookup_rcu_op_compare / __d_rehash (5)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 7aac71907bde Merge tag 'nfs-for-6.17-3' of git://git.linux..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=120d2b12580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6e0c213d0735f5dd
dashboard link: https://syzkaller.appspot.com/bug?extid=0c6b844bf515243f3689
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/a8ada750d318/disk-7aac7190.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/dd09c39f7402/vmlinux-7aac7190.xz
kernel image: https://storage.googleapis.com/syzbot-assets/feb31eae0186/bzImage-7aac7190.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0c6b84...@syzkaller.appspotmail.com

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

read to 0xffff8881054c2910 of 8 bytes by task 3305 on cpu 1:
hlist_bl_unhashed include/linux/list_bl.h:54 [inline]
d_unhashed include/linux/dcache.h:361 [inline]
__d_lookup_rcu_op_compare+0x104/0x270 fs/dcache.c:2208
__d_lookup_rcu+0x28e/0x2a0 fs/dcache.c:2271
d_alloc_parallel+0x21b/0xc60 fs/dcache.c:2566
__lookup_slow+0x8c/0x250 fs/namei.c:1793
lookup_slow+0x3c/0x60 fs/namei.c:1825
walk_component fs/namei.c:2129 [inline]
link_path_walk+0x753/0x900 fs/namei.c:2497
path_openat+0x1de/0x2170 fs/namei.c:4042
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 0xffff8881054c2910 of 8 bytes by task 3304 on cpu 0:
hlist_bl_add_head_rcu include/linux/rculist_bl.h:81 [inline]
__d_rehash+0x9e/0x1f0 fs/dcache.c:2489
__d_add+0x393/0x4f0 fs/dcache.c:2712
d_splice_alias_ops+0xdc/0x280 fs/dcache.c:3034
proc_sys_lookup+0x1ed/0x310 fs/proc/proc_sysctl.c:544
__lookup_slow+0x193/0x250 fs/namei.c:1808
lookup_slow+0x3c/0x60 fs/namei.c:1825
walk_component fs/namei.c:2129 [inline]
link_path_walk+0x753/0x900 fs/namei.c:2497
path_openat+0x1de/0x2170 fs/namei.c:4042
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

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3304 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
==================================================================
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 1560 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 1560 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 netdevsim2 netdevsim0: renamed from eth0
netdevsim netdevsim2 netdevsim1: renamed from eth1
netdevsim netdevsim2 netdevsim2: renamed from eth2
netdevsim netdevsim2 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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