[moderation] [fs?] KCSAN: data-race in __d_lookup / __d_rehash (11)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d2a43e7f89da Merge tag 'hardening-v7.0-rc6' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1580d06a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=3a78dd265deac3a9
dashboard link: https://syzkaller.appspot.com/bug?extid=967862f014d1ff91b6de
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
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/d8475b185c6b/disk-d2a43e7f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/738f2095b357/vmlinux-d2a43e7f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/47b59b07887c/bzImage-d2a43e7f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+967862...@syzkaller.appspotmail.com

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

write to 0xffff88810061dcd0 of 8 bytes by task 3311 on cpu 0:
hlist_bl_add_head_rcu include/linux/rculist_bl.h:81 [inline]
__d_rehash+0x9e/0x1f0 fs/dcache.c:2544
__d_add+0x344/0x4a0 fs/dcache.c:2769
d_splice_alias_ops+0xdc/0x320 fs/dcache.c:3110
proc_sys_lookup+0x1ed/0x310 fs/proc/proc_sysctl.c:544
__lookup_slow+0x19d/0x260 fs/namei.c:1916
lookup_slow+0x3c/0x60 fs/namei.c:1933
walk_component fs/namei.c:2279 [inline]
link_path_walk+0x946/0xe30 fs/namei.c:2647
path_openat+0x1c6/0x2050 fs/namei.c:4826
do_file_open+0x16c/0x290 fs/namei.c:4859
do_sys_openat2+0x94/0x130 fs/open.c:1366
do_sys_open fs/open.c:1372 [inline]
__do_sys_openat fs/open.c:1388 [inline]
__se_sys_openat fs/open.c:1383 [inline]
__x64_sys_openat+0xf2/0x120 fs/open.c:1383
x64_sys_call+0x1e39/0x3020 arch/x86/include/generated/asm/syscalls_64.h:258
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88810061dcd0 of 8 bytes by task 3308 on cpu 1:
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:2455
lookup_fast+0x5e/0x320 fs/namei.c:1874
walk_component fs/namei.c:2275 [inline]
link_path_walk+0x51c/0xe30 fs/namei.c:2647
path_openat+0x1c6/0x2050 fs/namei.c:4826
do_file_open+0x16c/0x290 fs/namei.c:4859
do_sys_openat2+0x94/0x130 fs/open.c:1366
do_sys_open fs/open.c:1372 [inline]
__do_sys_openat fs/open.c:1388 [inline]
__se_sys_openat fs/open.c:1383 [inline]
__x64_sys_openat+0xf2/0x120 fs/open.c:1383
x64_sys_call+0x1e39/0x3020 arch/x86/include/generated/asm/syscalls_64.h:258
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff88823761f4b8 -> 0xffff88810061db48

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3308 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================
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 netdevsim4 netdevsim0: renamed from eth0
netdevsim netdevsim4 netdevsim1: renamed from eth1
netdevsim netdevsim4 netdevsim2: renamed from eth2
netdevsim netdevsim4 netdevsim3: renamed from eth3
8021q: adding VLAN 0 to HW filter on device bond0
8021q: adding VLAN 0 to HW filter on device team0
hsr0: Slave B (hsr_slave_1) is not up; please bring it up to get a fully working HSR network
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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