syzbot

map[ReproOpts:{
	"pkg/osutil": {
		"pid": 12310,
		"uid": 0,
		"gid": 0,
		"groups": null
	}
} ReproSyz:r0 = socket(0x2, 0x2, 0x0)
bind(r0, &(0x7f0000000000)={0x2, 0x4e22, @local}, 0x10)
connect(r0, &(0x7f0000000040)={0x2, 0x4e22, @remote}, 0x10)
r1 = socket(0x18, 0x2, 0x1)
connect(r1, &(0x7f0000000080)={0x18, 0x1, {0x0, r0, {0x2, 0x4e22, @remote}, 0x0, 0x0, 0x0, 0x0}}, 0x26)
r2 = openat(0xffffffffffffff9c, &(0x7f0000000100)='/dev/nbd0\x00', 0x2, 0x0)
r3 = socket(0x1, 0x2, 0x0)
ioctl$NBD_SET_SOCK(r2, 0xab00, r3)
ioctl$NBD_SET_SIZE(r2, 0xab01, 0x1000)
write(r2, &(0x7f0000000200)='a', 0x1)
r4 = openat(0xffffffffffffff9c, &(0x7f0000000300)='/sys/block/nbd0/queue/scheduler\x00', 0x2, 0x0)
r5 = memfd_create(&(0x7f0000000400)='sched\x00', 0x0)
write(r5, &(0x7f0000000500)='none\x00', 0x5)
sendfile(r4, r5, 0x0, 0x5)
r6 = memfd_create(&(0x7f0000000600)='sched2\x00', 0x0)
write(r6, &(0x7f0000000700)='mq-deadline\x00', 0xc)
sendfile(r4, r6, 0x0, 0xc)
 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/ad90d25d1cad28a7674b1e711b5c23966d1f050f]

map[KernelObj:/usr/local/google/home/dvyukov/syzkaller/agent/workdir/cache/build/eb842fa8519961a1bbfcc0a2d6a6e55107ffea9c]

gemini-3-pro-preview

map[ReproOpts:{
	"pkg/osutil": {
		"pid": 12310,
		"uid": 0,
		"gid": 0,
		"groups": null
	}
}]

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: possible deadlock in kernfs_unlink_sibling

Original Crash Report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.3.1348/12310 is trying to acquire lock:
ffff88801cef0220 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_unlink_sibling+0xa3/0x320 fs/kernfs/dir.c:424

but task is already holding lock:
ffff88801cef0188 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_remove fs/kernfs/dir.c:1549 [inline]
ffff88801cef0188 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_remove+0x2f/0x50 fs/kernfs/dir.c:1540

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #10 (&root->kernfs_rwsem){++++}-{4:4}:
       down_write+0x92/0x200 kernel/locking/rwsem.c:1590
       kernfs_add_one+0x38/0x840 fs/kernfs/dir.c:791
       kernfs_create_dir_ns+0xfc/0x1a0 fs/kernfs/dir.c:1093
       internal_create_group+0x34d/0xf30 fs/sysfs/group.c:170
       cpuhp_invoke_callback+0x3d5/0xa10 kernel/cpu.c:195
       cpuhp_issue_call+0x1c0/0x980 kernel/cpu.c:2365
       __cpuhp_setup_state_cpuslocked+0x3a1/0x7b0 kernel/cpu.c:2511
       __cpuhp_setup_state+0xf4/0x300 kernel/cpu.c:2540
       do_one_initcall+0x123/0x6e0 init/main.c:1283
       do_initcall_level init/main.c:1345 [inline]
       do_initcalls init/main.c:1361 [inline]
       do_basic_setup init/main.c:1380 [inline]
       kernel_init_freeable+0x5c8/0x920 init/main.c:1593
       kernel_init+0x1c/0x2b0 init/main.c:1483
       ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #9 (cpuhp_state_mutex){+.+.}-{4:4}:

-> #8 (cpu_hotplug_lock){++++}-{0:0}:
       percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
       percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
       cpus_read_lock+0x42/0x160 kernel/cpu.c:491
       static_key_slow_inc+0x12/0x30 kernel/jump_label.c:190
       udp_tunnel_encap_enable include/net/udp_tunnel.h:203 [inline]
       setup_udp_tunnel_sock+0x39b/0x680 net/ipv4/udp_tunnel_core.c:92
       l2tp_tunnel_register+0x9c8/0xbe0 net/l2tp/l2tp_core.c:1679
       pppol2tp_tunnel_get.constprop.0+0x3f0/0x540 net/l2tp/l2tp_ppp.c:662
       pppol2tp_connect+0xb1b/0x1ce0 net/l2tp/l2tp_ppp.c:710
       __sys_connect_file+0x141/0x1a0 net/socket.c:2102
       __sys_connect+0x13b/0x160 net/socket.c:2121
       __do_sys_connect net/socket.c:2127 [inline]
       __se_sys_connect net/socket.c:2124 [inline]
       __x64_sys_connect+0x72/0xb0 net/socket.c:2124
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #7 (sk_lock-AF_INET){+.+.}-{0:0}:
       lock_sock_nested+0x41/0xf0 net/core/sock.c:3720
       lock_sock include/net/sock.h:1679 [inline]
       inet_shutdown+0x67/0x440 net/ipv4/af_inet.c:907
       nbd_mark_nsock_dead+0xae/0x5d0 drivers/block/nbd.c:319
       recv_work+0x671/0xa80 drivers/block/nbd.c:1024
       process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3263
       process_scheduled_works kernel/workqueue.c:3346 [inline]
       worker_thread+0x6c8/0xf10 kernel/workqueue.c:3427
       kthread+0x3c5/0x780 kernel/kthread.c:463
       ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #6 (&nsock->tx_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x193/0x1060 kernel/locking/mutex.c:760
       nbd_handle_cmd drivers/block/nbd.c:1146 [inline]
       nbd_queue_rq+0x423/0x12d0 drivers/block/nbd.c:1210
       blk_mq_dispatch_rq_list+0x416/0x1e20 block/blk-mq.c:2129
       __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
       blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
       __blk_mq_sched_dispatch_requests+0xcb7/0x15f0 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd8/0x1b0 block/blk-mq-sched.c:329
       blk_mq_run_hw_queue+0x239/0x670 block/blk-mq.c:2367
       blk_mq_dispatch_list+0x514/0x1310 block/blk-mq.c:2928
       blk_mq_flush_plug_list block/blk-mq.c:2976 [inline]
       blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2948
       __blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1225
       blk_finish_plug block/blk-core.c:1252 [inline]
       blk_finish_plug block/blk-core.c:1249 [inline]
       __submit_bio+0x545/0x690 block/blk-core.c:651
       __submit_bio_noacct_mq block/blk-core.c:724 [inline]
       submit_bio_noacct_nocheck+0x53d/0xc10 block/blk-core.c:755
       submit_bio_noacct+0x5bd/0x1f60 block/blk-core.c:879
       submit_bh fs/buffer.c:2829 [inline]
       block_read_full_folio+0x4db/0x850 fs/buffer.c:2461
       filemap_read_folio+0xc8/0x2a0 mm/filemap.c:2444
       do_read_cache_folio+0x263/0x5c0 mm/filemap.c:4036
       read_mapping_folio include/linux/pagemap.h:999 [inline]
       read_part_sector+0xd4/0x370 block/partitions/core.c:722
       adfspart_check_ICS+0x93/0x940 block/partitions/acorn.c:360
       check_partition block/partitions/core.c:141 [inline]
       blk_add_partitions block/partitions/core.c:589 [inline]
       bdev_disk_changed+0x723/0x1520 block/partitions/core.c:693
       blkdev_get_whole+0x187/0x290 block/bdev.c:748
       bdev_open+0x2c7/0xe40 block/bdev.c:957
       blkdev_open+0x34e/0x4f0 block/fops.c:701
       do_dentry_open+0x982/0x1530 fs/open.c:965
       vfs_open+0x82/0x3f0 fs/open.c:1097
       do_open fs/namei.c:3975 [inline]
       path_openat+0x1de4/0x2cb0 fs/namei.c:4134
       do_filp_open+0x20b/0x470 fs/namei.c:4161
       do_sys_openat2+0x11b/0x1d0 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+0x174/0x210 fs/open.c:1463
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #5 (&cmd->lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x193/0x1060 kernel/locking/mutex.c:760
       nbd_queue_rq+0xbd/0x12d0 drivers/block/nbd.c:1202
       blk_mq_dispatch_rq_list+0x416/0x1e20 block/blk-mq.c:2129
       __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
       blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
       __blk_mq_sched_dispatch_requests+0xcb7/0x15f0 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd8/0x1b0 block/blk-mq-sched.c:329
       blk_mq_run_hw_queue+0x239/0x670 block/blk-mq.c:2367
       blk_mq_dispatch_list+0x514/0x1310 block/blk-mq.c:2928
       blk_mq_flush_plug_list block/blk-mq.c:2976 [inline]
       blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2948
       __blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1225
       blk_finish_plug block/blk-core.c:1252 [inline]
       blk_finish_plug block/blk-core.c:1249 [inline]
       __submit_bio+0x545/0x690 block/blk-core.c:651
       __submit_bio_noacct_mq block/blk-core.c:724 [inline]
       submit_bio_noacct_nocheck+0x53d/0xc10 block/blk-core.c:755
       submit_bio_noacct+0x5bd/0x1f60 block/blk-core.c:879
       submit_bh fs/buffer.c:2829 [inline]
       block_read_full_folio+0x4db/0x850 fs/buffer.c:2461
       filemap_read_folio+0xc8/0x2a0 mm/filemap.c:2444
       do_read_cache_folio+0x263/0x5c0 mm/filemap.c:4036
       read_mapping_folio include/linux/pagemap.h:999 [inline]
       read_part_sector+0xd4/0x370 block/partitions/core.c:722
       adfspart_check_ICS+0x93/0x940 block/partitions/acorn.c:360
       check_partition block/partitions/core.c:141 [inline]
       blk_add_partitions block/partitions/core.c:589 [inline]
       bdev_disk_changed+0x723/0x1520 block/partitions/core.c:693
       blkdev_get_whole+0x187/0x290 block/bdev.c:748
       bdev_open+0x2c7/0xe40 block/bdev.c:957
       blkdev_open+0x34e/0x4f0 block/fops.c:701
       do_dentry_open+0x982/0x1530 fs/open.c:965
       vfs_open+0x82/0x3f0 fs/open.c:1097
       do_open fs/namei.c:3975 [inline]
       path_openat+0x1de4/0x2cb0 fs/namei.c:4134
       do_filp_open+0x20b/0x470 fs/namei.c:4161
       do_sys_openat2+0x11b/0x1d0 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+0x174/0x210 fs/open.c:1463
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (set->srcu){.+.+}-{0:0}:
       srcu_lock_sync include/linux/srcu.h:173 [inline]
       __synchronize_srcu+0xa1/0x290 kernel/rcu/srcutree.c:1439
       blk_mq_wait_quiesce_done block/blk-mq.c:283 [inline]
       blk_mq_wait_quiesce_done block/blk-mq.c:280 [inline]
       blk_mq_quiesce_queue block/blk-mq.c:303 [inline]
       blk_mq_quiesce_queue+0x149/0x1b0 block/blk-mq.c:298
       elevator_switch+0x17d/0x810 block/elevator.c:588
       elevator_change+0x391/0x5d0 block/elevator.c:691
       elevator_set_default+0x2e9/0x380 block/elevator.c:767
       blk_register_queue+0x384/0x4e0 block/blk-sysfs.c:942
       __add_disk+0x74a/0xf00 block/genhd.c:528
       add_disk_fwnode+0x13f/0x5d0 block/genhd.c:597
       add_disk include/linux/blkdev.h:775 [inline]
       nbd_dev_add+0x783/0xbb0 drivers/block/nbd.c:1987
       nbd_init+0x1a2/0x3c0 drivers/block/nbd.c:2702
       do_one_initcall+0x123/0x6e0 init/main.c:1283
       do_initcall_level init/main.c:1345 [inline]
       do_initcalls init/main.c:1361 [inline]
       do_basic_setup init/main.c:1380 [inline]
       kernel_init_freeable+0x5c8/0x920 init/main.c:1593
       kernel_init+0x1c/0x2b0 init/main.c:1483
       ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #3 (&q->elevator_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x193/0x1060 kernel/locking/mutex.c:760
       elevator_change+0x17d/0x5d0 block/elevator.c:689
       elv_iosched_store+0x315/0x3c0 block/elevator.c:824
       queue_attr_store+0x26b/0x310 block/blk-sysfs.c:869
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
       kernfs_fop_write_iter+0x3af/0x570 fs/kernfs/file.c:352
       iter_file_splice_write+0xa24/0x12e0 fs/splice.c:738
       do_splice_from fs/splice.c:938 [inline]
       direct_splice_actor+0x192/0x6c0 fs/splice.c:1161
       splice_direct_to_actor+0x345/0xa30 fs/splice.c:1105
       do_splice_direct_actor fs/splice.c:1204 [inline]
       do_splice_direct+0x174/0x240 fs/splice.c:1230
       do_sendfile+0xb06/0xe50 fs/read_write.c:1370
       __do_sys_sendfile64 fs/read_write.c:1431 [inline]
       __se_sys_sendfile64 fs/read_write.c:1417 [inline]
       __x64_sys_sendfile64+0x1d8/0x220 fs/read_write.c:1417
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&q->q_usage_counter(io)#64){++++}-{0:0}:
       blk_alloc_queue+0x619/0x760 block/blk-core.c:461
       blk_mq_alloc_queue+0x172/0x280 block/blk-mq.c:4399
       __blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4446
       nbd_dev_add+0x492/0xbb0 drivers/block/nbd.c:1957
       nbd_init+0x1a2/0x3c0 drivers/block/nbd.c:2702
       do_one_initcall+0x123/0x6e0 init/main.c:1283
       do_initcall_level init/main.c:1345 [inline]
       do_initcalls init/main.c:1361 [inline]
       do_basic_setup init/main.c:1380 [inline]
       kernel_init_freeable+0x5c8/0x920 init/main.c:1593
       kernel_init+0x1c/0x2b0 init/main.c:1483
       ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 (fs_reclaim){+.+.}-{0:0}:
       __fs_reclaim_acquire mm/page_alloc.c:4264 [inline]
       fs_reclaim_acquire+0x102/0x150 mm/page_alloc.c:4278
       might_alloc include/linux/sched/mm.h:318 [inline]
       slab_pre_alloc_hook mm/slub.c:4929 [inline]
       slab_alloc_node mm/slub.c:5264 [inline]
       kmem_cache_alloc_noprof+0x5b/0x6e0 mm/slub.c:5295
       __kernfs_iattrs+0x124/0x3e0 fs/kernfs/inode.c:36
       kernfs_iattrs fs/kernfs/inode.c:61 [inline]
       __kernfs_setattr+0x4d/0x3c0 fs/kernfs/inode.c:74
       kernfs_iop_setattr+0xda/0x120 fs/kernfs/inode.c:128
       notify_change+0x6d2/0x12a0 fs/attr.c:546
       do_truncate+0x1d7/0x230 fs/open.c:68
       handle_truncate fs/namei.c:3596 [inline]
       do_open fs/namei.c:3979 [inline]
       path_openat+0x2678/0x2cb0 fs/namei.c:4134
       do_filp_open+0x20b/0x470 fs/namei.c:4161
       do_sys_openat2+0x11b/0x1d0 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+0x174/0x210 fs/open.c:1463
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&root->kernfs_iattr_rwsem){++++}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x126f/0x1c90 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
       down_write+0x92/0x200 kernel/locking/rwsem.c:1590
       kernfs_unlink_sibling+0xa3/0x320 fs/kernfs/dir.c:424
       __kernfs_remove+0x2c0/0x8a0 fs/kernfs/dir.c:1514
       kernfs_remove fs/kernfs/dir.c:1550 [inline]
       kernfs_remove+0x37/0x50 fs/kernfs/dir.c:1540
       sysfs_remove_dir+0xc8/0x100 fs/sysfs/dir.c:101
       __kobject_del+0xe2/0x1f0 lib/kobject.c:604
       kobject_del lib/kobject.c:627 [inline]
       kobject_del+0x3f/0x60 lib/kobject.c:619
       elv_unregister_queue block/elevator.c:503 [inline]
       elevator_change_done+0x56b/0x6a0 block/elevator.c:646
       elevator_change+0x30b/0x5d0 block/elevator.c:695
       elv_iosched_store+0x315/0x3c0 block/elevator.c:824
       queue_attr_store+0x26b/0x310 block/blk-sysfs.c:869
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
       kernfs_fop_write_iter+0x3af/0x570 fs/kernfs/file.c:352
       iter_file_splice_write+0xa24/0x12e0 fs/splice.c:738
       do_splice_from fs/splice.c:938 [inline]
       direct_splice_actor+0x192/0x6c0 fs/splice.c:1161
       splice_direct_to_actor+0x345/0xa30 fs/splice.c:1105
       do_splice_direct_actor fs/splice.c:1204 [inline]
       do_splice_direct+0x174/0x240 fs/splice.c:1230
       do_sendfile+0xb06/0xe50 fs/read_write.c:1370
       __do_sys_sendfile64 fs/read_write.c:1431 [inline]
       __se_sys_sendfile64 fs/read_write.c:1417 [inline]
       __x64_sys_sendfile64+0x1d8/0x220 fs/read_write.c:1417
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  &root->kernfs_iattr_rwsem --> cpuhp_state_mutex --> &root->kernfs_rwsem

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&root->kernfs_rwsem);
                               lock(cpuhp_state_mutex);
                               lock(&root->kernfs_rwsem);
  lock(&root->kernfs_iattr_rwsem);

 *** DEADLOCK ***

5 locks held by syz.3.1348/12310:
 #0: ffff88807b8f2420 (sb_writers#7){.+.+}-{0:0}, at: splice_direct_to_actor+0x345/0xa30 fs/splice.c:1105
 #1: ffff888064716088 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x28f/0x570 fs/kernfs/file.c:343
 #2: ffff8880257dbd28 (kn->active#232){.+.+}-{0:0}, at: kernfs_get_active_of fs/kernfs/file.c:80 [inline]
 #2: ffff8880257dbd28 (kn->active#232){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x2ff/0x570 fs/kernfs/file.c:344
 #3: ffff8880267739c8 (&set->update_nr_hwq_lock){++++}-{4:4}, at: elv_iosched_store+0x35f/0x3c0 block/elevator.c:822
 #4: ffff88801cef0188 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_remove fs/kernfs/dir.c:1549 [inline]
 #4: ffff88801cef0188 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_remove+0x2f/0x50 fs/kernfs/dir.c:1540

stack backtrace:
CPU: 1 UID: 0 PID: 12310 Comm: syz.3.1348 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x275/0x350 kernel/locking/lockdep.c:2043
 check_noncircular+0x14c/0x170 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x126f/0x1c90 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
 down_write+0x92/0x200 kernel/locking/rwsem.c:1590
 kernfs_unlink_sibling+0xa3/0x320 fs/kernfs/dir.c:424
 __kernfs_remove+0x2c0/0x8a0 fs/kernfs/dir.c:1514
 kernfs_remove fs/kernfs/dir.c:1550 [inline]
 kernfs_remove+0x37/0x50 fs/kernfs/dir.c:1540
 sysfs_remove_dir+0xc8/0x100 fs/sysfs/dir.c:101
 __kobject_del+0xe2/0x1f0 lib/kobject.c:604
 kobject_del lib/kobject.c:627 [inline]
 kobject_del+0x3f/0x60 lib/kobject.c:619
 elv_unregister_queue block/elevator.c:503 [inline]
 elevator_change_done+0x56b/0x6a0 block/elevator.c:646
 elevator_change+0x30b/0x5d0 block/elevator.c:695
 elv_iosched_store+0x315/0x3c0 block/elevator.c:824
 queue_attr_store+0x26b/0x310 block/blk-sysfs.c:869
 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
 kernfs_fop_write_iter+0x3af/0x570 fs/kernfs/file.c:352
 iter_file_splice_write+0xa24/0x12e0 fs/splice.c:738
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x192/0x6c0 fs/splice.c:1161
 splice_direct_to_actor+0x345/0xa30 fs/splice.c:1105
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0x174/0x240 fs/splice.c:1230
 do_sendfile+0xb06/0xe50 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64 fs/read_write.c:1417 [inline]
 __x64_sys_sendfile64+0x1d8/0x220 fs/read_write.c:1417
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6fc7f8f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f6fc8dbb038 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f6fc81e6180 RCX: 00007f6fc7f8f749
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000002
RBP: 00007f6fc8013f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000009 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6fc81e6218 R14: 00007f6fc81e6180 R15: 00007ffe5e8c43a8
 </TASK>


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

r0 = socket(0x2, 0x2, 0x0)
bind(r0, &(0x7f0000000000)={0x2, 0x4e22, @local}, 0x10)
connect(r0, &(0x7f0000000040)={0x2, 0x4e22, @remote}, 0x10)
r1 = socket(0x18, 0x2, 0x1)
connect(r1, &(0x7f0000000080)={0x18, 0x1, {0x0, r0, {0x2, 0x4e22, @remote}, 0x0, 0x0, 0x0, 0x0}}, 0x26)
r2 = openat(0xffffffffffffff9c, &(0x7f0000000100)='/dev/nbd0\x00', 0x2, 0x0)
r3 = socket(0x1, 0x2, 0x0)
ioctl$NBD_SET_SOCK(r2, 0xab00, r3)
ioctl$NBD_SET_SIZE(r2, 0xab01, 0x1000)
write(r2, &(0x7f0000000200)='a', 0x1)
r4 = openat(0xffffffffffffff9c, &(0x7f0000000300)='/sys/block/nbd0/queue/scheduler\x00', 0x2, 0x0)
r5 = memfd_create(&(0x7f0000000400)='sched\x00', 0x0)
write(r5, &(0x7f0000000500)='none\x00', 0x5)
sendfile(r4, r5, 0x0, 0x5)
r6 = memfd_create(&(0x7f0000000600)='sched2\x00', 0x0)
write(r6, &(0x7f0000000700)='mq-deadline\x00', 0xc)
sendfile(r4, r6, 0x0, 0xc)

gemini-3-pro-preview

							input: 11598
							output: 66
							thoughts: 17656
						

**Deadlock Reproducer: Kernfs Lock Cycle**

Okay, so the goal is to trigger a deadlock in `kernfs_unlink_sibling` related to the crash report involving `kernfs_iattr_rwsem`, `cpuhp_state_mutex`, and `kernfs_rwsem`. The syzkaller program I need to construct will target the circular dependency described: `&root->kernfs_iattr_rwsem` --> `cpuhp_state_mutex` --> `&root->kernfs_rwsem`, and the reported trace `syz.3.1348/12310` which acquires `kernfs_iattr_rwsem` while holding `kernfs_rwsem`. This appears during `kernfs_remove`, where `kernfs_rwsem` is taken, then a subsequent call to `kernfs_unlink_sibling` which tries for the `kernfs_iattr_rwsem`.

The crucial dependency is that `kernfs_remove` (and so `kernfs_unlink_sibling`) is a trigger for the new dependency `kernfs_rwsem` -> `kernfs_iattr_rwsem`. From the report, this seems to be driven by `sendfile` operations in sysfs, which calls into the block layer. Specifically, the crash report indicates that writing to the `queue/scheduler` file of a block device triggers the elevator change which then calls `kernfs_remove`. The key is to exercise this "new" dependency path (`kernfs_rwsem` to `kernfs_iattr_rwsem`).

To ensure that the rest of the dependencies that lead to this path are also active, I need to incorporate operations to activate the reported older dependency chain, notably:

1.  A path of `kernfs_iattr_rwsem` to `fs_reclaim`. This might involve allocations and `kmem_cache_alloc`, which happens within `kernfs_iop_setattr`.
2.  A path involving `sk_lock` through `cpu_hotplug_lock` to `cpuhp_state_mutex`, which creates a longer dependency chain. The stack trace mentions `nbd_queue_rq`, `nbd_handle_cmd`, which involves socket operations related to NBD, then L2TP to involve `sk_lock` -> `cpu_hotplug_lock`.

Therefore, the strategy will be:

1.  Set up an NBD (network block device) device. Specifically, the stack trace mentions `nbd_queue_rq`. So I need to set up NBD. This involves `open`, `socketpair`, `NBD_SET_SOCK`, `NBD_SET_SIZE` etc. and some kind of NBD I/O.
2.  Set up an L2TP tunnel. Specifically, the `pppol2tp_connect` path is mentioned, which should help to form `sk_lock` to `cpu_hotplug_lock` chain. This means `socket`, `bind`, and `connect` calls with the appropriate addresses for a L2TP tunnel.
3.  Write to the `/sys/block/nbd0/queue/scheduler` sysfs file using `sendfile` syscall and try to switch elevators, with "none" and "mq-deadline". This will trigger the path.

The syzkaller program I create will therefore:

1.  Establish an L2TP connection via sockets, specifically creating an AF\_INET UDP socket and then an AF\_PPPOX socket to get to the required `connect` call.
2.  Set up the NBD device and its associated socket. This involves the necessary `ioctl` calls to configure the NBD device. This setup will be required to get the necessary block layer locking. This means `socket`, `open`, `ioctl` (with `NBD_SET_SOCK`, `NBD_SET_SIZE`, and some `write`). I'll use `socket` and `ioctl` with the appropriate arguments.
3.  Then I will call `sendfile` on `/sys/block/nbd0/queue/scheduler` with "none" and "mq-deadline", which should trigger the elevator change and subsequent removal, hitting the deadlock. I will create a memfd for the "scheduler" string write.

The key to triggering the circular dependency is to make sure the lock dependencies are recorded. The `kernfs_remove` call will be the "new" dependency, and the L2TP setup and NBD I/O will try to exercise the path to make the "old" dependency active for the `lockdep` checker. If all parts of the chain are present, then writing to the scheduler file using `sendfile` should complete the deadlock. It's a bit of a dance

map[ReproOpts:{
	"pkg/osutil": {
		"pid": 12310,
		"uid": 0,
		"gid": 0,
		"groups": null
	}
}]

map[ReproOpts:{
	"pkg/osutil": {
		"pid": 12310,
		"uid": 0,
		"gid": 0,
		"groups": null
	}
}]

gemini-3-pro-preview

							input: 30409
							output: 604
							thoughts: 0