syzbot


KCSAN: data-race in __d_lookup / __d_rehash (10)

Status: moderation: reported on 2025/12/20 11:31
Subsystems: fs
[Documentation on labels]
Reported-by: syzbot+8df9d8f0a279a10acd12@syzkaller.appspotmail.com
First crash: 2d23h, last: 2d23h
Similar bugs (9)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in __d_lookup / __d_rehash (8) ext4 6 8 494d 611d 0/29 auto-obsoleted due to no activity on 2024/09/19 14:50
upstream KCSAN: data-race in __d_lookup / __d_rehash (6) fs 6 1 850d 850d 0/29 auto-obsoleted due to no activity on 2023/09/29 22:29
upstream KCSAN: data-race in __d_lookup / __d_rehash (4) ext4 6 1 968d 968d 0/29 auto-obsoleted due to no activity on 2023/06/04 03:50
upstream KCSAN: data-race in __d_lookup / __d_rehash fs 6 1 2229d 2229d 0/29 auto-closed as invalid on 2020/01/24 17:56
upstream KCSAN: data-race in __d_lookup / __d_rehash (3) fs 6 1 1139d 1139d 0/29 auto-obsoleted due to no activity on 2022/12/14 23:50
upstream KCSAN: data-race in __d_lookup / __d_rehash (2) fs 6 1 1333d 1333d 0/29 auto-closed as invalid on 2022/06/04 08:25
upstream KCSAN: data-race in __d_lookup / __d_rehash (9) fs 6 21 75d 360d 0/29 auto-obsoleted due to no activity on 2025/12/04 01:21
upstream KCSAN: data-race in __d_lookup / __d_rehash (5) ext4 6 2 908d 910d 0/29 auto-obsoleted due to no activity on 2023/08/02 16:55
upstream KCSAN: data-race in __d_lookup / __d_rehash (7) ext4 6 1 803d 803d 0/29 auto-obsoleted due to no activity on 2023/11/15 16:47

Sample crash report:
==================================================================
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

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/12/20 11:31 upstream dd9b004b7ff3 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_lookup / __d_rehash
* Struck through repros no longer work on HEAD.