syzbot

map[ReproOpts:{
    "threaded": true,
    "collide": true,
    "repeat": true,
    "procs": 8,
    "sandbox": "namespace",
    "fault_call": -1,
    "fault_nth": 0
} ReproSyz:unshare(0x40000000)
r0 = openat(0xffffffffffffff9c, &(0x7f0000000000)='/proc/sys/net/ipv4/conf/all\x00', 0x0, 0x0)
unshare(0x40000000)
openat(r0, &(0x7f0000000080)='forwarding\x00', 0x0, 0x0)
openat(r0, &(0x7f00000000a0)='rp_filter\x00', 0x0, 0x0)
openat(r0, &(0x7f00000000c0)='accept_redirects\x00', 0x0, 0x0)
openat(r0, &(0x7f00000000e0)='secure_redirects\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000100)='shared_media\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000120)='send_redirects\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000140)='accept_source_route\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000160)='mc_forwarding\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000180)='proxy_arp\x00', 0x0, 0x0)
openat(r0, &(0x7f00000001a0)='medium_id\x00', 0x0, 0x0)
openat(r0, &(0x7f00000001c0)='bootp_relay\x00', 0x0, 0x0)
openat(r0, &(0x7f00000001e0)='log_martians\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000200)='tag\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000220)='arp_filter\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000240)='arp_announce\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000260)='arp_ignore\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000280)='arp_accept\x00', 0x0, 0x0)
openat(r0, &(0x7f00000002a0)='arp_notify\x00', 0x0, 0x0)
openat(r0, &(0x7f00000002c0)='proxy_arp_pvlan\x00', 0x0, 0x0)
openat(r0, &(0x7f00000002e0)='disable_xfrm\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000300)='disable_policy\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000320)='force_igmp_version\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000340)='promote_secondaries\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000360)='route_localnet\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000380)='drop_unicast_in_l2_multicast\x00', 0x0, 0x0)
openat(r0, &(0x7f00000003a0)='drop_gratuitous_arp\x00', 0x0, 0x0)
openat(r0, &(0x7f00000003c0)='bc_forwarding\x00', 0x0, 0x0)
openat(r0, &(0x7f00000003e0)='arp_evict_nocarrier\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000400)='arp_managed\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000420)='igmpv2_unsolicited_report_interval\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000440)='igmpv3_unsolicited_report_interval\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000460)='ignore_routes_with_linkdown\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000480)='drop_metadata_skb\x00', 0x0, 0x0)
openat(r0, &(0x7f00000004a0)='txrehash\x00', 0x0, 0x0)
openat(r0, &(0x7f00000004c0)='forwarding\x00', 0x0, 0x0)
openat(r0, &(0x7f00000004e0)='rp_filter\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000500)='accept_redirects\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000520)='secure_redirects\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000540)='shared_media\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000560)='send_redirects\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000580)='accept_source_route\x00', 0x0, 0x0)
openat(r0, &(0x7f00000005a0)='mc_forwarding\x00', 0x0, 0x0)
openat(r0, &(0x7f00000005c0)='proxy_arp\x00', 0x0, 0x0)
openat(r0, &(0x7f00000005e0)='medium_id\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000600)='bootp_relay\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000620)='log_martians\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000640)='tag\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000660)='arp_filter\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000680)='arp_announce\x00', 0x0, 0x0)
openat(r0, &(0x7f00000006a0)='arp_ignore\x00', 0x0, 0x0)
openat(r0, &(0x7f00000006c0)='arp_accept\x00', 0x0, 0x0)
openat(r0, &(0x7f00000006e0)='arp_notify\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000700)='proxy_arp_pvlan\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000720)='disable_xfrm\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000740)='disable_policy\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000760)='force_igmp_version\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000780)='promote_secondaries\x00', 0x0, 0x0)
openat(r0, &(0x7f00000007a0)='route_localnet\x00', 0x0, 0x0)
openat(r0, &(0x7f00000007c0)='drop_unicast_in_l2_multicast\x00', 0x0, 0x0)
openat(r0, &(0x7f00000007e0)='drop_gratuitous_arp\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000800)='bc_forwarding\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000820)='arp_evict_nocarrier\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000840)='arp_managed\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000860)='igmpv2_unsolicited_report_interval\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000880)='igmpv3_unsolicited_report_interval\x00', 0x0, 0x0)
openat(r0, &(0x7f00000008a0)='ignore_routes_with_linkdown\x00', 0x0, 0x0)
openat(r0, &(0x7f00000008c0)='drop_metadata_skb\x00', 0x0, 0x0)
openat(r0, &(0x7f00000008e0)='txrehash\x00', 0x0, 0x0)
 SyzkallerCommit:31e9c887f7dc24e04b3ca70d0d54fc34141844b0]

map[DescriptionFiles:[acpi_thermal_rel.txt aio.txt auto.txt binfmt.txt bpf.txt bpf_prog.txt bpf_trace.txt cgroup.txt damon.txt dev_ashmem.txt dev_bifrost.txt dev_binder.txt dev_binderfs.txt dev_block.txt dev_bsg.txt dev_bus_usb.txt dev_camx.txt dev_cdrom.txt dev_cec.txt dev_char_usb.txt dev_comedi.txt dev_dma_heap.txt dev_dri.txt dev_dsp.txt dev_dvb_demux.txt dev_dvb_dvr.txt dev_dvb_frontend.txt dev_fb.txt dev_floppy.txt dev_hidraw.txt dev_i2c.txt dev_i915.txt dev_img_rogue.txt dev_infiniband_rdma.txt dev_infiniband_rdma_cm.txt dev_input.txt dev_iommu.txt dev_kvm.txt dev_kvm_amd64.txt dev_kvm_arm64.txt dev_kvm_extra.txt dev_kvm_riscv64.txt dev_loop.txt dev_mali.txt dev_media.txt dev_msm.txt dev_msr.txt dev_nbd.txt dev_net_tun.txt dev_panthor.txt dev_ppp.txt dev_ptmx.txt dev_ptp.txt dev_qat_adf_ctl.txt dev_qrtr_tun.txt dev_random.txt dev_rfkill.txt dev_rtc.txt dev_sequencer.txt dev_sg.txt dev_snapshot.txt dev_snd_control.txt dev_snd_hw.txt dev_snd_midi.txt dev_snd_pcm.txt dev_snd_seq.txt dev_snd_timer.txt dev_sr.txt dev_sw_sync.txt dev_tlk_device.txt dev_trusty.txt dev_udmabuf.txt dev_uhid.txt dev_uinput.txt dev_usb_hiddev.txt dev_usbmon.txt dev_userio.txt dev_vfio.txt dev_vga_arbiter.txt dev_vhci.txt dev_video4linux.txt dev_video4linux_vim2m.txt dev_virtual_nci.txt dev_vtpm.txt fanotify.txt filesystem.txt fs_9p.txt fs_fuse.txt fs_incfs.txt fs_ioctl.txt fs_ioctl_autofs.txt fs_ioctl_btrfs.txt fs_ioctl_ext4.txt fs_ioctl_f2fs.txt fs_ioctl_fat.txt fs_ioctl_fscrypt.txt fs_ioctl_fsverity.txt fs_ioctl_xfs.txt futex.txt hafnium.txt inotify.txt io_uring.txt ipc.txt key.txt kfuzztest.txt l2cap.txt landlock.txt lsm.txt namespaces.txt net_80211.txt netfilter.txt netfilter_arp.txt netfilter_bridge.txt netfilter_ipv4.txt netfilter_ipv6.txt netfilter_ipvs.txt netfilter_targets.txt pagemap_ioctl.txt perf.txt prctl.txt quotactl.txt seccomp.txt security_apparmor.txt security_selinux.txt security_smack.txt socket.txt socket_alg.txt socket_ax25.txt socket_bluetooth.txt socket_caif.txt socket_can.txt socket_ieee802154.txt socket_inet.txt socket_inet6.txt socket_inet_dccp.txt socket_inet_icmp.txt socket_inet_igmp.txt socket_inet_l2tp.txt socket_inet_sctp.txt socket_inet_tcp.txt socket_inet_udp.txt socket_ip_tunnel.txt socket_isdn.txt socket_kcm.txt socket_key.txt socket_llc.txt socket_netlink.txt socket_netlink_audit.txt socket_netlink_crypto.txt socket_netlink_generic.txt socket_netlink_generic_80211.txt socket_netlink_generic_batadv.txt socket_netlink_generic_devlink.txt socket_netlink_generic_ethtool.txt socket_netlink_generic_fou.txt socket_netlink_generic_gtp.txt socket_netlink_generic_mptcp.txt socket_netlink_generic_net_dm.txt socket_netlink_generic_netlabel.txt socket_netlink_generic_nfc.txt socket_netlink_generic_seg6.txt socket_netlink_generic_smc.txt socket_netlink_generic_team.txt socket_netlink_generic_wireguard.txt socket_netlink_netfilter.txt socket_netlink_netfilter_acct.txt socket_netlink_netfilter_conntrack.txt socket_netlink_netfilter_conntrack_exp.txt socket_netlink_netfilter_conntrack_helper.txt socket_netlink_netfilter_ipset.txt socket_netlink_netfilter_log.txt socket_netlink_netfilter_nft_compat.txt socket_netlink_netfilter_nftables.txt socket_netlink_netfilter_osf.txt socket_netlink_netfilter_queue.txt socket_netlink_netfilter_timeout.txt socket_netlink_rdma.txt socket_netlink_route.txt socket_netlink_route_sched.txt socket_netlink_route_sched_retired.txt socket_netlink_sock_diag.txt socket_netlink_xfrm.txt socket_netrom.txt socket_nfc.txt socket_nvme_of_tcp.txt socket_packet.txt socket_phonet.txt socket_pppox.txt socket_qipcrtr.txt socket_rds.txt socket_rose.txt socket_rxrpc.txt socket_tipc.txt socket_tipc_netlink.txt socket_unix.txt socket_vnet.txt socket_x25.txt socket_xdp.txt sys.txt uffd.txt usbip.txt vmw_vmci.txt vnet.txt vnet_mptcp.txt vusb.txt watch_queue.txt xattr.txt] SyzkallerCommit:31e9c887f7dc24e04b3ca70d0d54fc34141844b0]

map[KernelSrc:/usr/local/google/home/dvyukov/syzkaller/agent/workdir/cache/src/442656ac8be766ac08d507e9d55d7e172d7ca2ec]

map[KernelObj:/usr/local/google/home/dvyukov/syzkaller/agent/workdir/cache/build/d5e7fe031ef17fcd9d75f07422941eb5162b2fe8]

gemini-3-pro-preview

map[ReproOpts:{
    "threaded": true,
    "collide": true,
    "repeat": true,
    "procs": 8,
    "sandbox": "namespace",
    "fault_call": -1,
    "fault_nth": 0
}]

You are an expert in linux kernel fuzzing. Your goal is to write a syzkaller program to trigger a specific bug.
Print only the syz program that could be executed directly, without backticks.




Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

Bug Title: KCSAN: data-race in __d_drop / __d_lookup

Original Crash Report:
==================================================================
BUG: KCSAN: data-race in __d_drop / __d_lookup

write to 0xffff8881076ccb50 of 8 bytes by task 31 on cpu 1:
 __hlist_bl_del include/linux/list_bl.h:128 [inline]
 ___d_drop fs/dcache.c:568 [inline]
 __d_drop+0xf7/0x240 fs/dcache.c:575
 d_invalidate+0x50/0x1d0 fs/dcache.c:1701
 proc_invalidate_siblings_dcache+0x1c8/0x2b0 fs/proc/inode.c:142
 proc_sys_invalidate_dcache fs/proc/proc_sysctl.c:289 [inline]
 start_unregistering fs/proc/proc_sysctl.c:316 [inline]
 drop_sysctl_table+0xbd/0x270 fs/proc/proc_sysctl.c:1517
 drop_sysctl_table+0x1cb/0x270 fs/proc/proc_sysctl.c:1524
 drop_sysctl_table+0x1cb/0x270 fs/proc/proc_sysctl.c:1524
 drop_sysctl_table+0x1cb/0x270 fs/proc/proc_sysctl.c:1524
 unregister_sysctl_table+0x30/0x50 fs/proc/proc_sysctl.c:1542
 unregister_net_sysctl_table+0x15/0x20 net/sysctl_net.c:177
 __devinet_sysctl_unregister net/ipv4/devinet.c:2700 [inline]
 devinet_exit_net+0x10a/0x190 net/ipv4/devinet.c:2863
 ops_exit_list net/core/net_namespace.c:199 [inline]
 ops_undo_list+0x285/0x420 net/core/net_namespace.c:252
 cleanup_net+0x31c/0x550 net/core/net_namespace.c:696
 process_one_work kernel/workqueue.c:3257 [inline]
 process_scheduled_works+0x4cd/0x9d0 kernel/workqueue.c:3340
 worker_thread+0x6bc/0x8b0 kernel/workqueue.c:3421
 kthread+0x488/0x510 kernel/kthread.c:463
 ret_from_fork+0x148/0x280 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

read to 0xffff8881076ccb50 of 8 bytes by task 3039 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:2455
 lookup_fast+0x5e/0x320 fs/namei.c:1824
 walk_component fs/namei.c:2225 [inline]
 link_path_walk+0x51c/0xe30 fs/namei.c:2597
 path_openat+0x1bf/0x23c0 fs/namei.c:4792
 do_filp_open+0x15d/0x280 fs/namei.c:4823
 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+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff88811a898d88 -> 0xffff88811a96da88

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3039 Comm: dhcpcd Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


The list of existing description files:
acpi_thermal_rel.txt
aio.txt
auto.txt
binfmt.txt
bpf.txt
bpf_prog.txt
bpf_trace.txt
cgroup.txt
damon.txt
dev_ashmem.txt
dev_bifrost.txt
dev_binder.txt
dev_binderfs.txt
dev_block.txt
dev_bsg.txt
dev_bus_usb.txt
dev_camx.txt
dev_cdrom.txt
dev_cec.txt
dev_char_usb.txt
dev_comedi.txt
dev_dma_heap.txt
dev_dri.txt
dev_dsp.txt
dev_dvb_demux.txt
dev_dvb_dvr.txt
dev_dvb_frontend.txt
dev_fb.txt
dev_floppy.txt
dev_hidraw.txt
dev_i2c.txt
dev_i915.txt
dev_img_rogue.txt
dev_infiniband_rdma.txt
dev_infiniband_rdma_cm.txt
dev_input.txt
dev_iommu.txt
dev_kvm.txt
dev_kvm_amd64.txt
dev_kvm_arm64.txt
dev_kvm_extra.txt
dev_kvm_riscv64.txt
dev_loop.txt
dev_mali.txt
dev_media.txt
dev_msm.txt
dev_msr.txt
dev_nbd.txt
dev_net_tun.txt
dev_panthor.txt
dev_ppp.txt
dev_ptmx.txt
dev_ptp.txt
dev_qat_adf_ctl.txt
dev_qrtr_tun.txt
dev_random.txt
dev_rfkill.txt
dev_rtc.txt
dev_sequencer.txt
dev_sg.txt
dev_snapshot.txt
dev_snd_control.txt
dev_snd_hw.txt
dev_snd_midi.txt
dev_snd_pcm.txt
dev_snd_seq.txt
dev_snd_timer.txt
dev_sr.txt
dev_sw_sync.txt
dev_tlk_device.txt
dev_trusty.txt
dev_udmabuf.txt
dev_uhid.txt
dev_uinput.txt
dev_usb_hiddev.txt
dev_usbmon.txt
dev_userio.txt
dev_vfio.txt
dev_vga_arbiter.txt
dev_vhci.txt
dev_video4linux.txt
dev_video4linux_vim2m.txt
dev_virtual_nci.txt
dev_vtpm.txt
fanotify.txt
filesystem.txt
fs_9p.txt
fs_fuse.txt
fs_incfs.txt
fs_ioctl.txt
fs_ioctl_autofs.txt
fs_ioctl_btrfs.txt
fs_ioctl_ext4.txt
fs_ioctl_f2fs.txt
fs_ioctl_fat.txt
fs_ioctl_fscrypt.txt
fs_ioctl_fsverity.txt
fs_ioctl_xfs.txt
futex.txt
hafnium.txt
inotify.txt
io_uring.txt
ipc.txt
key.txt
kfuzztest.txt
l2cap.txt
landlock.txt
lsm.txt
namespaces.txt
net_80211.txt
netfilter.txt
netfilter_arp.txt
netfilter_bridge.txt
netfilter_ipv4.txt
netfilter_ipv6.txt
netfilter_ipvs.txt
netfilter_targets.txt
pagemap_ioctl.txt
perf.txt
prctl.txt
quotactl.txt
seccomp.txt
security_apparmor.txt
security_selinux.txt
security_smack.txt
socket.txt
socket_alg.txt
socket_ax25.txt
socket_bluetooth.txt
socket_caif.txt
socket_can.txt
socket_ieee802154.txt
socket_inet.txt
socket_inet6.txt
socket_inet_dccp.txt
socket_inet_icmp.txt
socket_inet_igmp.txt
socket_inet_l2tp.txt
socket_inet_sctp.txt
socket_inet_tcp.txt
socket_inet_udp.txt
socket_ip_tunnel.txt
socket_isdn.txt
socket_kcm.txt
socket_key.txt
socket_llc.txt
socket_netlink.txt
socket_netlink_audit.txt
socket_netlink_crypto.txt
socket_netlink_generic.txt
socket_netlink_generic_80211.txt
socket_netlink_generic_batadv.txt
socket_netlink_generic_devlink.txt
socket_netlink_generic_ethtool.txt
socket_netlink_generic_fou.txt
socket_netlink_generic_gtp.txt
socket_netlink_generic_mptcp.txt
socket_netlink_generic_net_dm.txt
socket_netlink_generic_netlabel.txt
socket_netlink_generic_nfc.txt
socket_netlink_generic_seg6.txt
socket_netlink_generic_smc.txt
socket_netlink_generic_team.txt
socket_netlink_generic_wireguard.txt
socket_netlink_netfilter.txt
socket_netlink_netfilter_acct.txt
socket_netlink_netfilter_conntrack.txt
socket_netlink_netfilter_conntrack_exp.txt
socket_netlink_netfilter_conntrack_helper.txt
socket_netlink_netfilter_ipset.txt
socket_netlink_netfilter_log.txt
socket_netlink_netfilter_nft_compat.txt
socket_netlink_netfilter_nftables.txt
socket_netlink_netfilter_osf.txt
socket_netlink_netfilter_queue.txt
socket_netlink_netfilter_timeout.txt
socket_netlink_rdma.txt
socket_netlink_route.txt
socket_netlink_route_sched.txt
socket_netlink_route_sched_retired.txt
socket_netlink_sock_diag.txt
socket_netlink_xfrm.txt
socket_netrom.txt
socket_nfc.txt
socket_nvme_of_tcp.txt
socket_packet.txt
socket_phonet.txt
socket_pppox.txt
socket_qipcrtr.txt
socket_rds.txt
socket_rose.txt
socket_rxrpc.txt
socket_tipc.txt
socket_tipc_netlink.txt
socket_unix.txt
socket_vnet.txt
socket_x25.txt
socket_xdp.txt
sys.txt
uffd.txt
usbip.txt
vmw_vmci.txt
vnet.txt
vnet_mptcp.txt
vusb.txt
watch_queue.txt
xattr.txt

unshare(0x40000000)
r0 = openat(0xffffffffffffff9c, &(0x7f0000000000)='/proc/sys/net/ipv4/conf/all\x00', 0x0, 0x0)
unshare(0x40000000)
openat(r0, &(0x7f0000000080)='forwarding\x00', 0x0, 0x0)
openat(r0, &(0x7f00000000a0)='rp_filter\x00', 0x0, 0x0)
openat(r0, &(0x7f00000000c0)='accept_redirects\x00', 0x0, 0x0)
openat(r0, &(0x7f00000000e0)='secure_redirects\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000100)='shared_media\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000120)='send_redirects\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000140)='accept_source_route\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000160)='mc_forwarding\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000180)='proxy_arp\x00', 0x0, 0x0)
openat(r0, &(0x7f00000001a0)='medium_id\x00', 0x0, 0x0)
openat(r0, &(0x7f00000001c0)='bootp_relay\x00', 0x0, 0x0)
openat(r0, &(0x7f00000001e0)='log_martians\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000200)='tag\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000220)='arp_filter\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000240)='arp_announce\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000260)='arp_ignore\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000280)='arp_accept\x00', 0x0, 0x0)
openat(r0, &(0x7f00000002a0)='arp_notify\x00', 0x0, 0x0)
openat(r0, &(0x7f00000002c0)='proxy_arp_pvlan\x00', 0x0, 0x0)
openat(r0, &(0x7f00000002e0)='disable_xfrm\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000300)='disable_policy\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000320)='force_igmp_version\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000340)='promote_secondaries\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000360)='route_localnet\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000380)='drop_unicast_in_l2_multicast\x00', 0x0, 0x0)
openat(r0, &(0x7f00000003a0)='drop_gratuitous_arp\x00', 0x0, 0x0)
openat(r0, &(0x7f00000003c0)='bc_forwarding\x00', 0x0, 0x0)
openat(r0, &(0x7f00000003e0)='arp_evict_nocarrier\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000400)='arp_managed\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000420)='igmpv2_unsolicited_report_interval\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000440)='igmpv3_unsolicited_report_interval\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000460)='ignore_routes_with_linkdown\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000480)='drop_metadata_skb\x00', 0x0, 0x0)
openat(r0, &(0x7f00000004a0)='txrehash\x00', 0x0, 0x0)
openat(r0, &(0x7f00000004c0)='forwarding\x00', 0x0, 0x0)
openat(r0, &(0x7f00000004e0)='rp_filter\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000500)='accept_redirects\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000520)='secure_redirects\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000540)='shared_media\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000560)='send_redirects\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000580)='accept_source_route\x00', 0x0, 0x0)
openat(r0, &(0x7f00000005a0)='mc_forwarding\x00', 0x0, 0x0)
openat(r0, &(0x7f00000005c0)='proxy_arp\x00', 0x0, 0x0)
openat(r0, &(0x7f00000005e0)='medium_id\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000600)='bootp_relay\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000620)='log_martians\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000640)='tag\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000660)='arp_filter\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000680)='arp_announce\x00', 0x0, 0x0)
openat(r0, &(0x7f00000006a0)='arp_ignore\x00', 0x0, 0x0)
openat(r0, &(0x7f00000006c0)='arp_accept\x00', 0x0, 0x0)
openat(r0, &(0x7f00000006e0)='arp_notify\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000700)='proxy_arp_pvlan\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000720)='disable_xfrm\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000740)='disable_policy\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000760)='force_igmp_version\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000780)='promote_secondaries\x00', 0x0, 0x0)
openat(r0, &(0x7f00000007a0)='route_localnet\x00', 0x0, 0x0)
openat(r0, &(0x7f00000007c0)='drop_unicast_in_l2_multicast\x00', 0x0, 0x0)
openat(r0, &(0x7f00000007e0)='drop_gratuitous_arp\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000800)='bc_forwarding\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000820)='arp_evict_nocarrier\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000840)='arp_managed\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000860)='igmpv2_unsolicited_report_interval\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000880)='igmpv3_unsolicited_report_interval\x00', 0x0, 0x0)
openat(r0, &(0x7f00000008a0)='ignore_routes_with_linkdown\x00', 0x0, 0x0)
openat(r0, &(0x7f00000008c0)='drop_metadata_skb\x00', 0x0, 0x0)
openat(r0, &(0x7f00000008e0)='txrehash\x00', 0x0, 0x0)

gemini-3-pro-preview

							input: 3214
							output: 77
							thoughts: 18417
						

**Reproducing the KCSAN Data Race in `__d_drop` / `__d_lookup`**

Okay, here's my breakdown. Based on the crash report, I believe the bug lies in a race condition where a KCSAN data race happens between reading and writing to the dcache entries related to the `/proc/sys` files, specifically when dealing with sysctls that pertain to network namespaces. The write happens during network namespace cleanup, and the read is during an `openat` operation. My plan is to create a syzkaller program that will reliably trigger this bug.

My initial hypothesis is that I need to create a new network namespace, access some sysctl files within that namespace (e.g. `/proc/sys/net/ipv4/conf/all/forwarding`), and then concurrently destroy the namespace. The race will occur when `cleanup_net`, triggered by namespace destruction, attempts to invalidate the dcache entries for those sysctls while another process or thread is attempting to look them up.

The crash report mentions `devinet_exit_net` and the associated unregistration of sysctl tables, indicating that it's related to the cleanup of a network namespace and the race happens when the namespace is destroyed. The strategy is now to create a scenario where the lookup to sysctl files overlaps with the netns cleanup. I have considered a few ways to do this. I'll need to figure out how to force cleanup while still having a file handle open to something in that namespace. I realized I don't need a complicated threading scheme; I can use a simple sequence using `unshare`.

I want the write (cleanup) to happen while a read (lookup) is ongoing. I can use `unshare` to create a new netns. I can get an `fd` to a sysctl directory in that netns (like `/proc/sys/net/ipv4/conf/all`). Then I can call `unshare` *again*, which will drop the reference to that old namespace. Now it's being cleaned up, and I can call `openat` (relative to the old `fd`) to lookup.

I can make this really simple with the following syzkaller program:

1.  `unshare(CLONE_NEWNET)`: Create a new network namespace, and I'm now in it.
2.  `openat(..., '/proc/sys/net/ipv4/conf/all', O_RDONLY)`: Open the sysctl directory in this new netns.
3.  `unshare(CLONE_NEWNET)`: Destroy the netns from step 1, by moving into a new one. This will trigger the cleanup.
4.  `openat(r0, "forwarding", ...)`: Now repeatedly attempt to `openat` different sysctl files in that directory.

My expectation is that the `unshare` will trigger the netns destruction, while `openat` will be attempting to look up in the dcache. Since `cleanup_net` is asynchronous (runs in a workqueue), there is a window for the race. I'll include `repeat=true` when running syzkaller so that it repeats this sequence, increasing the likelihood of the crash. I'll run this with multi-threaded execution using the `-threaded -collide` options to increase probability of hitting the race.

The final syzkaller program will be:
```
unshare(0x40000000)
r0 = openat(0xffffffffffffff9c, &(0x7f0000000000)='/proc/sys/net/ipv4/conf/all\x00', 0x0, 0x0)
unshare(0x40000000)
openat(r0, &(0x7f0000000080)='forwarding\x00', 0x0, 0x0)
openat(r0, &(0x7f00000000a0)='rp_filter\x00', 0x0, 0x0)
openat(r0, &(0x7f00000000c0)='accept_redirects\x00', 0x0, 0x0)
openat(r0, &(0x7f00000000e0)='secure_redirects\x00', 0x0, 0x0)
openat(r0, &(0x7f0000000100)='shared_media\x00', 0x

map[ReproOpts:{
    "threaded": true,
    "collide": true,
    "repeat": true,
    "procs": 8,
    "sandbox": "namespace",
    "fault_call": -1,
    "fault_nth": 0
}]

map[ReproOpts:{
    "threaded": true,
    "collide": true,
    "repeat": true,
    "procs": 8,
    "sandbox": "namespace",
    "fault_call": -1,
    "fault_nth": 0
}]

gemini-3-pro-preview

							input: 22808
							output: 3063
							thoughts: 0