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KCSAN: data-race in __d_lookup_rcu_op_compare / __d_rehash (4)

Status: moderation: reported on 2025/06/23 21:54
Subsystems: fs
[Documentation on labels]
Reported-by: syzbot+3ab1a6cc9e38e5519b26@syzkaller.appspotmail.com
First crash: 1d14h, last: 1d14h
Similar bugs (3)
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in __d_lookup_rcu_op_compare / __d_rehash (2) fs 3 218d 242d 0/29 auto-obsoleted due to no activity on 2025/01/13 18:14
upstream KCSAN: data-race in __d_lookup_rcu_op_compare / __d_rehash (3) fs 5 57d 135d 0/29 auto-obsoleted due to no activity on 2025/06/23 19:20
upstream KCSAN: data-race in __d_lookup_rcu_op_compare / __d_rehash fs 1 313d 313d 0/29 auto-obsoleted due to no activity on 2024/09/19 20:54

Sample crash report:
==================================================================
BUG: KCSAN: data-race in __d_lookup_rcu_op_compare / __d_rehash

read to 0xffff88810574c010 of 8 bytes by task 3307 on cpu 0:
 hlist_bl_unhashed include/linux/list_bl.h:54 [inline]
 d_unhashed include/linux/dcache.h:359 [inline]
 __d_lookup_rcu_op_compare+0x104/0x270 fs/dcache.c:2192
 __d_lookup_rcu+0x28e/0x2a0 fs/dcache.c:2255
 d_alloc_parallel+0x209/0xc40 fs/dcache.c:2544
 lookup_open fs/namei.c:3639 [inline]
 open_last_lookups fs/namei.c:3816 [inline]
 path_openat+0x6b5/0x2170 fs/namei.c:4052
 do_filp_open+0x109/0x230 fs/namei.c:4082
 do_sys_openat2+0xa6/0x110 fs/open.c:1437
 do_sys_open fs/open.c:1452 [inline]
 __do_sys_openat fs/open.c:1468 [inline]
 __se_sys_openat fs/open.c:1463 [inline]
 __x64_sys_openat+0xf2/0x120 fs/open.c:1463
 x64_sys_call+0x1af/0x2fb0 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 0xffff88810574c010 of 8 bytes by task 3309 on cpu 1:
 hlist_bl_add_head_rcu include/linux/rculist_bl.h:81 [inline]
 __d_rehash+0x9e/0x1f0 fs/dcache.c:2473
 __d_add+0x364/0x4c0 fs/dcache.c:2689
 d_splice_alias+0xd6/0x280 fs/dcache.c:3033
 proc_sys_lookup+0x1f6/0x320 fs/proc/proc_sysctl.c:545
 lookup_open fs/namei.c:3695 [inline]
 open_last_lookups fs/namei.c:3816 [inline]
 path_openat+0xcf3/0x2170 fs/namei.c:4052
 do_filp_open+0x109/0x230 fs/namei.c:4082
 do_sys_openat2+0xa6/0x110 fs/open.c:1437
 do_sys_open fs/open.c:1452 [inline]
 __do_sys_openat fs/open.c:1468 [inline]
 __se_sys_openat fs/open.c:1463 [inline]
 __x64_sys_openat+0xf2/0x120 fs/open.c:1463
 x64_sys_call+0x1af/0x2fb0 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: 1 UID: 0 PID: 3309 Comm: syz-executor Not tainted 6.16.0-rc3-syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================
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: Directory 'hsr0' with parent 'hsr' already present!
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
netdevsim netdevsim2 netdevsim0: set [1, 0] type 2 family 0 port 6081 - 0
netdevsim netdevsim2 netdevsim1: set [1, 0] type 2 family 0 port 6081 - 0
netdevsim netdevsim2 netdevsim2: set [1, 0] type 2 family 0 port 6081 - 0
netdevsim netdevsim2 netdevsim3: set [1, 0] type 2 family 0 port 6081 - 0
soft_limit_in_bytes is deprecated and will be removed. Please report your usecase to linux-mm@kvack.org if you depend on this functionality.

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/06/23 21:53 upstream 86731a2a651e e2f27c35 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_lookup_rcu_op_compare / __d_rehash
* Struck through repros no longer work on HEAD.