* [syzbot] [kernfs?] possible deadlock in kernfs_link_sibling (2)
@ 2026-03-17 17:33 syzbot
2026-08-26 19:33 ` syzbot
0 siblings, 1 reply; 8+ messages in thread
From: syzbot @ 2026-03-17 17:33 UTC (permalink / raw)
To: driver-core, gregkh, linux-kernel, syzkaller-bugs, tj
Hello,
syzbot found the following issue on:
HEAD commit: 2d1373e4246d Merge tag 'for-7.0-rc4-tag' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13ab3406580000
kernel config: https://syzkaller.appspot.com/x/.config?x=45cb3c58fd963c27
dashboard link: https://syzkaller.appspot.com/bug?extid=dd764a450d93885d847f
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b8f9fdb26fea/disk-2d1373e4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1f20580466c5/vmlinux-2d1373e4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f051fb6711e4/bzImage-2d1373e4.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+dd764a450d93885d847f@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G L
------------------------------------------------------
kworker/u9:1/11370 is trying to acquire lock:
ffff888019c4f2c0 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_link_sibling+0x46c/0x540 fs/kernfs/dir.c:394
but task is already holding lock:
ffff888019c4f238 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_add_one+0x41/0x5c0 fs/kernfs/dir.c:796
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #10 (&root->kernfs_rwsem){++++}-{4:4}:
down_write+0x3a/0x50 kernel/locking/rwsem.c:1590
kernfs_add_one+0x41/0x5c0 fs/kernfs/dir.c:796
kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1098
internal_create_group+0x425/0x1180 fs/sysfs/group.c:176
cpuhp_invoke_callback+0x445/0x860 kernel/cpu.c:194
cpuhp_issue_call+0x430/0x7a0 kernel/cpu.c:-1
__cpuhp_setup_state_cpuslocked+0x3d9/0x6b0 kernel/cpu.c:2507
__cpuhp_setup_state+0x3f/0x60 kernel/cpu.c:2536
do_one_initcall+0x250/0x8d0 init/main.c:1382
do_initcall_level+0x104/0x190 init/main.c:1444
do_initcalls+0x59/0xa0 init/main.c:1460
kernel_init_freeable+0x2a6/0x3e0 init/main.c:1692
kernel_init+0x1d/0x1d0 init/main.c:1582
ret_from_fork+0x51e/0xb90 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:490
static_key_slow_inc+0x12/0x30 kernel/jump_label.c:190
tcp_md5_do_add+0x1d4/0x390 net/ipv4/tcp_ipv4.c:1431
tcp_v6_parse_md5_keys+0x562/0x680 net/ipv6/tcp_ipv6.c:-1
do_tcp_setsockopt+0x12ee/0x2060 net/ipv4/tcp.c:4134
do_sock_setsockopt+0x17c/0x1b0 net/socket.c:2322
__sys_setsockopt net/socket.c:2347 [inline]
__do_sys_setsockopt net/socket.c:2353 [inline]
__se_sys_setsockopt net/socket.c:2350 [inline]
__x64_sys_setsockopt+0x143/0x1b0 net/socket.c:2350
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #7 (sk_lock-AF_INET6){+.+.}-{0:0}:
lock_sock_nested+0x3e/0x130 net/core/sock.c:3780
lock_sock include/net/sock.h:1709 [inline]
inet_shutdown+0x6a/0x390 net/ipv4/af_inet.c:919
nbd_mark_nsock_dead+0x2e9/0x560 drivers/block/nbd.c:318
recv_work+0x1c9d/0x1dc0 drivers/block/nbd.c:1021
process_one_work kernel/workqueue.c:3276 [inline]
process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x51e/0xb90 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/rtmutex_api.c:533 [inline]
mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:552
nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
nbd_queue_rq+0x37b/0x1100 drivers/block/nbd.c:1207
blk_mq_dispatch_rq_list+0xa77/0x1910 block/blk-mq.c:2148
__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+0xddb/0x1610 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xda/0x1a0 block/blk-mq-sched.c:329
blk_mq_run_hw_queue+0x368/0x520 block/blk-mq.c:2386
blk_mq_dispatch_list+0xd1f/0xe20 include/linux/spinlock_rt.h:-1
blk_mq_flush_plug_list+0x48d/0x570 block/blk-mq.c:2997
__blk_flush_plug+0x3ed/0x4d0 block/blk-core.c:1230
blk_finish_plug block/blk-core.c:1257 [inline]
__submit_bio+0x28d/0x580 block/blk-core.c:649
__submit_bio_noacct_mq block/blk-core.c:722 [inline]
submit_bio_noacct_nocheck+0x2f4/0xa70 block/blk-core.c:753
submit_bh fs/buffer.c:2826 [inline]
block_read_full_folio+0x599/0x830 fs/buffer.c:2444
filemap_read_folio+0x137/0x3b0 mm/filemap.c:2501
do_read_cache_folio+0x2bf/0x560 mm/filemap.c:4101
read_mapping_folio include/linux/pagemap.h:1028 [inline]
read_part_sector+0xb8/0x2b0 block/partitions/core.c:723
adfspart_check_ICS+0xa5/0xa40 block/partitions/acorn.c:360
check_partition block/partitions/core.c:142 [inline]
blk_add_partitions block/partitions/core.c:590 [inline]
bdev_disk_changed+0x7ba/0x1550 block/partitions/core.c:694
blkdev_get_whole+0x2e5/0x480 block/bdev.c:764
bdev_open+0x31e/0xcc0 block/bdev.c:973
blkdev_open+0x485/0x620 block/fops.c:697
do_dentry_open+0x83d/0x13e0 fs/open.c:949
vfs_open+0x3b/0x350 fs/open.c:1081
do_open fs/namei.c:4671 [inline]
path_openat+0x2e43/0x38a0 fs/namei.c:4830
do_file_open+0x23e/0x4a0 fs/namei.c:4859
do_sys_openat2+0x113/0x200 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+0x138/0x170 fs/open.c:1383
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #5 (&cmd->lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/rtmutex_api.c:533 [inline]
mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:552
nbd_queue_rq+0xc6/0x1100 drivers/block/nbd.c:1199
blk_mq_dispatch_rq_list+0xa77/0x1910 block/blk-mq.c:2148
__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+0xddb/0x1610 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xda/0x1a0 block/blk-mq-sched.c:329
blk_mq_run_hw_queue+0x368/0x520 block/blk-mq.c:2386
blk_mq_dispatch_list+0xd1f/0xe20 include/linux/spinlock_rt.h:-1
blk_mq_flush_plug_list+0x48d/0x570 block/blk-mq.c:2997
__blk_flush_plug+0x3ed/0x4d0 block/blk-core.c:1230
blk_finish_plug block/blk-core.c:1257 [inline]
__submit_bio+0x28d/0x580 block/blk-core.c:649
__submit_bio_noacct_mq block/blk-core.c:722 [inline]
submit_bio_noacct_nocheck+0x2f4/0xa70 block/blk-core.c:753
submit_bh fs/buffer.c:2826 [inline]
block_read_full_folio+0x599/0x830 fs/buffer.c:2444
filemap_read_folio+0x137/0x3b0 mm/filemap.c:2501
do_read_cache_folio+0x2bf/0x560 mm/filemap.c:4101
read_mapping_folio include/linux/pagemap.h:1028 [inline]
read_part_sector+0xb8/0x2b0 block/partitions/core.c:723
adfspart_check_ICS+0xa5/0xa40 block/partitions/acorn.c:360
check_partition block/partitions/core.c:142 [inline]
blk_add_partitions block/partitions/core.c:590 [inline]
bdev_disk_changed+0x7ba/0x1550 block/partitions/core.c:694
blkdev_get_whole+0x2e5/0x480 block/bdev.c:764
bdev_open+0x31e/0xcc0 block/bdev.c:973
blkdev_open+0x485/0x620 block/fops.c:697
do_dentry_open+0x83d/0x13e0 fs/open.c:949
vfs_open+0x3b/0x350 fs/open.c:1081
do_open fs/namei.c:4671 [inline]
path_openat+0x2e43/0x38a0 fs/namei.c:4830
do_file_open+0x23e/0x4a0 fs/namei.c:4859
do_sys_openat2+0x113/0x200 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+0x138/0x170 fs/open.c:1383
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 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:199 [inline]
__synchronize_srcu+0xca/0x3e0 kernel/rcu/srcutree.c:1505
elevator_switch+0x1e8/0x7a0 block/elevator.c:576
elevator_change+0x2cc/0x450 block/elevator.c:681
elevator_set_default+0x36c/0x430 block/elevator.c:754
blk_register_queue+0x366/0x430 block/blk-sysfs.c:946
__add_disk+0x677/0xd50 block/genhd.c:528
add_disk_fwnode+0xfb/0x480 block/genhd.c:597
add_disk include/linux/blkdev.h:785 [inline]
nbd_dev_add+0x72c/0xb50 drivers/block/nbd.c:1984
nbd_init+0x168/0x1f0 drivers/block/nbd.c:2692
do_one_initcall+0x250/0x8d0 init/main.c:1382
do_initcall_level+0x104/0x190 init/main.c:1444
do_initcalls+0x59/0xa0 init/main.c:1460
kernel_init_freeable+0x2a6/0x3e0 init/main.c:1692
kernel_init+0x1d/0x1d0 init/main.c:1582
ret_from_fork+0x51e/0xb90 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/rtmutex_api.c:533 [inline]
mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:552
elevator_change+0x1b3/0x450 block/elevator.c:679
elevator_set_none+0xb5/0x140 block/elevator.c:769
blk_mq_elv_switch_none block/blk-mq.c:5110 [inline]
__blk_mq_update_nr_hw_queues block/blk-mq.c:5155 [inline]
blk_mq_update_nr_hw_queues+0x607/0x1a80 block/blk-mq.c:5220
nbd_start_device+0x17f/0xb20 drivers/block/nbd.c:1489
nbd_genl_connect+0x1651/0x1c80 drivers/block/nbd.c:2239
genl_family_rcv_msg_doit+0x22a/0x330 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x61c/0x7a0 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x232/0x4b0 net/netlink/af_netlink.c:2550
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
netlink_unicast+0x831/0x9f0 net/netlink/af_netlink.c:1344
netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1894
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg net/socket.c:742 [inline]
____sys_sendmsg+0x94c/0x9c0 net/socket.c:2592
___sys_sendmsg+0x2a5/0x360 net/socket.c:2646
__sys_sendmsg net/socket.c:2678 [inline]
__do_sys_sendmsg net/socket.c:2683 [inline]
__se_sys_sendmsg net/socket.c:2681 [inline]
__x64_sys_sendmsg+0x1c3/0x2a0 net/socket.c:2681
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #2 (&q->q_usage_counter(io)#75){++++}-{0:0}:
blk_alloc_queue+0x54e/0x690 block/blk-core.c:461
blk_mq_alloc_queue block/blk-mq.c:4429 [inline]
__blk_mq_alloc_disk+0x197/0x390 block/blk-mq.c:4476
nbd_dev_add+0x499/0xb50 drivers/block/nbd.c:1954
nbd_genl_connect+0x965/0x1c80 drivers/block/nbd.c:2125
genl_family_rcv_msg_doit+0x22a/0x330 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x61c/0x7a0 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x232/0x4b0 net/netlink/af_netlink.c:2550
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
netlink_unicast+0x831/0x9f0 net/netlink/af_netlink.c:1344
netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1894
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg net/socket.c:742 [inline]
____sys_sendmsg+0x94c/0x9c0 net/socket.c:2592
___sys_sendmsg+0x2a5/0x360 net/socket.c:2646
__sys_sendmsg net/socket.c:2678 [inline]
__do_sys_sendmsg net/socket.c:2683 [inline]
__se_sys_sendmsg net/socket.c:2681 [inline]
__x64_sys_sendmsg+0x1c3/0x2a0 net/socket.c:2681
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #1 (fs_reclaim){+.+.}-{0:0}:
__fs_reclaim_acquire mm/page_alloc.c:4348 [inline]
fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4362
might_alloc include/linux/sched/mm.h:317 [inline]
slab_pre_alloc_hook mm/slub.c:4489 [inline]
slab_alloc_node mm/slub.c:4843 [inline]
kmem_cache_alloc_noprof+0x44/0x680 mm/slub.c:4873
__kernfs_iattrs+0xdf/0x340 fs/kernfs/inode.c:36
kernfs_iattrs fs/kernfs/inode.c:61 [inline]
__kernfs_setattr fs/kernfs/inode.c:74 [inline]
kernfs_iop_setattr+0xea/0x3f0 fs/kernfs/inode.c:128
notify_change+0xc18/0xf60 fs/attr.c:556
do_truncate+0x1c2/0x250 fs/open.c:68
handle_truncate fs/namei.c:4279 [inline]
do_open fs/namei.c:4675 [inline]
path_openat+0x2fc4/0x38a0 fs/namei.c:4830
do_file_open+0x23e/0x4a0 fs/namei.c:4859
do_sys_openat2+0x113/0x200 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+0x138/0x170 fs/open.c:1383
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868
down_write+0x3a/0x50 kernel/locking/rwsem.c:1590
kernfs_link_sibling+0x46c/0x540 fs/kernfs/dir.c:394
kernfs_add_one+0x1ca/0x5c0 fs/kernfs/dir.c:815
kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1098
sysfs_create_dir_ns+0x12f/0x2a0 fs/sysfs/dir.c:59
create_dir lib/kobject.c:73 [inline]
kobject_add_internal+0x631/0xd10 lib/kobject.c:240
kobject_add_varg lib/kobject.c:374 [inline]
kobject_add+0x163/0x240 lib/kobject.c:426
device_add+0x408/0xb80 drivers/base/core.c:3627
hci_conn_add_sysfs+0xd5/0x210 net/bluetooth/hci_sysfs.c:48
hci_conn_complete_evt+0x77a/0x11d0 net/bluetooth/hci_event.c:3195
hci_event_func net/bluetooth/hci_event.c:7784 [inline]
hci_event_packet+0x805/0x12c0 net/bluetooth/hci_event.c:7838
hci_rx_work+0x3ee/0x1030 net/bluetooth/hci_core.c:4077
process_one_work kernel/workqueue.c:3276 [inline]
process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
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 ***
4 locks held by kworker/u9:1/11370:
#0: ffff888033cf8938 ((wq_completion)hci0#2){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3251 [inline]
#0: ffff888033cf8938 ((wq_completion)hci0#2){+.+.}-{0:0}, at: process_scheduled_works+0xa52/0x18c0 kernel/workqueue.c:3359
#1: ffffc90005fefc40 ((work_completion)(&hdev->rx_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3252 [inline]
#1: ffffc90005fefc40 ((work_completion)(&hdev->rx_work)){+.+.}-{0:0}, at: process_scheduled_works+0xa8d/0x18c0 kernel/workqueue.c:3359
#2: ffff8880392140b0 (&hdev->lock){+.+.}-{4:4}, at: hci_conn_complete_evt+0xbb/0x11d0 net/bluetooth/hci_event.c:3113
#3: ffff888019c4f238 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_add_one+0x41/0x5c0 fs/kernfs/dir.c:796
stack backtrace:
CPU: 0 UID: 0 PID: 11370 Comm: kworker/u9:1 Tainted: G L syzkaller #0 PREEMPT_{RT,(full)}
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: hci0 hci_rx_work
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043
check_noncircular+0x12e/0x150 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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868
down_write+0x3a/0x50 kernel/locking/rwsem.c:1590
kernfs_link_sibling+0x46c/0x540 fs/kernfs/dir.c:394
kernfs_add_one+0x1ca/0x5c0 fs/kernfs/dir.c:815
kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1098
sysfs_create_dir_ns+0x12f/0x2a0 fs/sysfs/dir.c:59
create_dir lib/kobject.c:73 [inline]
kobject_add_internal+0x631/0xd10 lib/kobject.c:240
kobject_add_varg lib/kobject.c:374 [inline]
kobject_add+0x163/0x240 lib/kobject.c:426
device_add+0x408/0xb80 drivers/base/core.c:3627
hci_conn_add_sysfs+0xd5/0x210 net/bluetooth/hci_sysfs.c:48
hci_conn_complete_evt+0x77a/0x11d0 net/bluetooth/hci_event.c:3195
hci_event_func net/bluetooth/hci_event.c:7784 [inline]
hci_event_packet+0x805/0x12c0 net/bluetooth/hci_event.c:7838
hci_rx_work+0x3ee/0x1030 net/bluetooth/hci_core.c:4077
process_one_work kernel/workqueue.c:3276 [inline]
process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title
If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)
If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report
If you want to undo deduplication, reply with:
#syz undup
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [syzbot] [kernfs?] possible deadlock in kernfs_link_sibling (2)
2026-03-17 17:33 [syzbot] [kernfs?] possible deadlock in kernfs_link_sibling (2) syzbot
@ 2026-08-26 19:33 ` syzbot
2026-08-26 22:49 ` Hillf Danton
` (2 more replies)
0 siblings, 3 replies; 8+ messages in thread
From: syzbot @ 2026-08-26 19:33 UTC (permalink / raw)
To: bugs, davidkrehwinkel, discussions, driver-core, gregkh,
linux-kernel, lore, mail, syzkaller-bugs, tj, vrp-test
syzbot has found a reproducer for the following issue on:
HEAD commit: 818bebeb63dd drm/xe: Don't hand out the flat CCS storage a..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=10059625580000
kernel config: https://syzkaller.appspot.com/x/.config?x=ccca94d2c01b9e78
dashboard link: https://syzkaller.appspot.com/bug?extid=dd764a450d93885d847f
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13de8d49580000
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+dd764a450d93885d847f@syzkaller.appspotmail.com
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
kworker/3:0/34 is trying to acquire lock:
ffff88801d6a5a10 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_link_sibling+0x555/0x850 fs/kernfs/dir.c:411
but task is already holding lock:
ffff88801d6a5980 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_add_one+0x38/0xaa0 fs/kernfs/dir.c:825
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #9 (&root->kernfs_rwsem){++++}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
kernfs_add_one+0x38/0xaa0 fs/kernfs/dir.c:825
kernfs_create_dir_ns+0x157/0x2b0 fs/kernfs/dir.c:1130
internal_create_group+0x36f/0xfb0 fs/sysfs/group.c:176
cpuhp_invoke_callback+0x3b4/0x9a0 kernel/cpu.c:194
cpuhp_issue_call+0x1b8/0x970 kernel/cpu.c:2354
__cpuhp_setup_state_cpuslocked+0x431/0x880 kernel/cpu.c:2507
__cpuhp_setup_state+0xf7/0x2f0 kernel/cpu.c:2536
do_one_initcall+0x11c/0x6f0 init/main.c:1353
do_initcall_level init/main.c:1415 [inline]
do_initcalls init/main.c:1431 [inline]
do_basic_setup init/main.c:1451 [inline]
kernel_init_freeable+0x6ea/0x7b0 init/main.c:1666
kernel_init+0x21/0x1e0 init/main.c:1556
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #8 (cpuhp_state_mutex){+.+.}-{4:4}:
-> #7 (cpu_hotplug_lock){++++}-{0:0}:
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
cpus_read_lock+0x42/0x170 kernel/cpu.c:490
static_key_slow_inc+0x12/0x30 kernel/jump_label.c:190
nbd_genl_reconnect_sock_cb+0x39f/0x990 drivers/block/nbd.c:1377
nbd_genl_foreach_sock+0x2ab/0x3e0 drivers/block/nbd.c:2152
nbd_genl_reconfigure+0x861/0xde0 drivers/block/nbd.c:2477
genl_family_rcv_msg_doit+0x214/0x300 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x560/0x800 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2556
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1900
sock_sendmsg_nosec net/socket.c:800 [inline]
__sock_sendmsg net/socket.c:815 [inline]
__sys_sendto+0x48b/0x4e0 net/socket.c:2281
__do_sys_sendto net/socket.c:2288 [inline]
__se_sys_sendto net/socket.c:2284 [inline]
__x64_sys_sendto+0xe0/0x1c0 net/socket.c:2284
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #6 (&nsock->tx_lock){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821
nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
nbd_queue_rq+0x42d/0xfa0 drivers/block/nbd.c:1207
blk_mq_dispatch_rq_list+0x428/0x1e60 block/blk-mq.c:2117
__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+0xcea/0x1620 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
blk_mq_run_work_fn+0x135/0x380 block/blk-mq.c:2531
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3387
process_scheduled_works kernel/workqueue.c:3470 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3551
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #5 (&cmd->lock){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821
nbd_queue_rq+0xba/0xfa0 drivers/block/nbd.c:1199
blk_mq_dispatch_rq_list+0x428/0x1e60 block/blk-mq.c:2117
__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+0xcea/0x1620 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
blk_mq_run_work_fn+0x135/0x380 block/blk-mq.c:2531
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3387
process_scheduled_works kernel/workqueue.c:3470 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3551
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #4 (set->srcu){.+.+}-{0:0}:
lock_sync kernel/locking/lockdep.c:5934 [inline]
lock_sync+0x9d/0x110 kernel/locking/lockdep.c:5922
srcu_lock_sync include/linux/srcu.h:199 [inline]
__synchronize_srcu+0xa2/0x300 kernel/rcu/srcutree.c:1481
blk_mq_wait_quiesce_done block/blk-mq.c:284 [inline]
blk_mq_wait_quiesce_done block/blk-mq.c:281 [inline]
blk_mq_quiesce_queue block/blk-mq.c:304 [inline]
blk_mq_quiesce_queue+0x149/0x1c0 block/blk-mq.c:299
elevator_switch+0x17b/0x7e0 block/elevator.c:576
elevator_change+0x352/0x530 block/elevator.c:681
elevator_set_default+0x29e/0x360 block/elevator.c:754
blk_register_queue+0x48e/0x630 block/blk-sysfs.c:992
__add_disk+0x73f/0xe40 block/genhd.c:524
add_disk_fwnode+0x118/0x480 block/genhd.c:593
add_disk include/linux/blkdev.h:798 [inline]
nbd_dev_add+0x779/0xb10 drivers/block/nbd.c:2026
nbd_init+0x2c5/0x2e0 drivers/block/nbd.c:2743
do_one_initcall+0x11c/0x6f0 init/main.c:1353
do_initcall_level init/main.c:1415 [inline]
do_initcalls init/main.c:1431 [inline]
do_basic_setup init/main.c:1451 [inline]
kernel_init_freeable+0x6ea/0x7b0 init/main.c:1666
kernel_init+0x21/0x1e0 init/main.c:1556
ret_from_fork+0x730/0xd60 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}:
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821
elevator_change+0x1bc/0x530 block/elevator.c:679
elevator_set_none+0x92/0xf0 block/elevator.c:769
blk_mq_elv_switch_none block/blk-mq.c:5102 [inline]
__blk_mq_update_nr_hw_queues block/blk-mq.c:5147 [inline]
blk_mq_update_nr_hw_queues+0x4c1/0x15f0 block/blk-mq.c:5212
nbd_start_device+0x1a6/0xbd0 drivers/block/nbd.c:1530
nbd_genl_connect+0xfc2/0x1760 drivers/block/nbd.c:2310
genl_family_rcv_msg_doit+0x214/0x300 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x560/0x800 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2556
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1900
sock_sendmsg_nosec net/socket.c:800 [inline]
__sock_sendmsg net/socket.c:815 [inline]
__sys_sendto+0x48b/0x4e0 net/socket.c:2281
__do_sys_sendto net/socket.c:2288 [inline]
__se_sys_sendto net/socket.c:2284 [inline]
__x64_sys_sendto+0xe0/0x1c0 net/socket.c:2284
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #2 (&q->q_usage_counter(io)#49){++++}-{0:0}:
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
blk_alloc_queue+0x610/0x790 block/blk-core.c:504
blk_mq_alloc_queue+0x174/0x290 block/blk-mq.c:4420
__blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4467
nbd_dev_add+0x491/0xb10 drivers/block/nbd.c:1996
nbd_init+0x2c5/0x2e0 drivers/block/nbd.c:2743
do_one_initcall+0x11c/0x6f0 init/main.c:1353
do_initcall_level init/main.c:1415 [inline]
do_initcalls init/main.c:1431 [inline]
do_basic_setup init/main.c:1451 [inline]
kernel_init_freeable+0x6ea/0x7b0 init/main.c:1666
kernel_init+0x21/0x1e0 init/main.c:1556
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #1 (fs_reclaim){+.+.}-{0:0}:
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
__fs_reclaim_acquire mm/page_alloc.c:4375 [inline]
fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4389
might_alloc include/linux/sched/mm.h:314 [inline]
slab_pre_alloc_hook mm/slub.c:4539 [inline]
slab_alloc_node mm/slub.c:4899 [inline]
kmem_cache_alloc_noprof+0x63/0x6a0 mm/slub.c:4933
__kernfs_iattrs+0x126/0x450 fs/kernfs/inode.c:36
kernfs_iattrs fs/kernfs/inode.c:60 [inline]
__kernfs_setattr+0x4d/0x3c0 fs/kernfs/inode.c:73
kernfs_iop_setattr+0xda/0x130 fs/kernfs/inode.c:127
notify_change+0xb25/0x1330 fs/attr.c:556
do_truncate+0x1df/0x240 fs/open.c:68
handle_truncate fs/namei.c:4300 [inline]
do_open fs/namei.c:4841 [inline]
path_openat+0x1e6d/0x2440 fs/namei.c:5000
do_file_open+0x20e/0x430 fs/namei.c:5029
do_sys_openat2+0x10f/0x1e0 fs/open.c:1417
do_sys_open fs/open.c:1423 [inline]
__do_sys_openat fs/open.c:1439 [inline]
__se_sys_openat fs/open.c:1434 [inline]
__x64_sys_openat+0x12d/0x210 fs/open.c:1434
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #0 (&root->kernfs_iattr_rwsem){++++}-{4:4}:
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3181
check_prevs_add kernel/locking/lockdep.c:3300 [inline]
validate_chain kernel/locking/lockdep.c:3924 [inline]
__lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5253
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
kernfs_link_sibling+0x555/0x850 fs/kernfs/dir.c:411
kernfs_add_one+0x1e7/0xaa0 fs/kernfs/dir.c:844
kernfs_create_dir_ns+0x157/0x2b0 fs/kernfs/dir.c:1130
sysfs_create_dir_ns+0x13a/0x2b0 fs/sysfs/dir.c:59
create_dir lib/kobject.c:73 [inline]
kobject_add_internal+0x2c8/0x930 lib/kobject.c:240
kobject_add_varg lib/kobject.c:374 [inline]
kobject_add+0x16a/0x1e0 lib/kobject.c:426
device_add+0x294/0x1970 drivers/base/core.c:3699
hid_add_device+0x2bf/0x440 drivers/hid/hid-core.c:3065
uhid_device_add_worker+0x3a/0x70 drivers/hid/uhid.c:73
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3387
process_scheduled_works kernel/workqueue.c:3470 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3551
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
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 ***
locks held by kworker/3:0/34: 3, last CPU#3:
#0: ffff88801c0aa940 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x1466/0x1b10 kernel/workqueue.c:3362
#1: ffffc900006dfd08 ((work_completion)(&uhid->worker)){+.+.}-{0:0}, at: process_one_work+0xa2c/0x1b10 kernel/workqueue.c:3363
#2: ffff88801d6a5980 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_add_one+0x38/0xaa0 fs/kernfs/dir.c:825
stack backtrace:
CPU: 3 UID: 0 PID: 34 Comm: kworker/3:0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Workqueue: events uhid_device_add_worker
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
print_circular_bug.cold+0x178/0x1be kernel/locking/lockdep.c:2059
check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2191
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3181
check_prevs_add kernel/locking/lockdep.c:3300 [inline]
validate_chain kernel/locking/lockdep.c:3924 [inline]
__lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5253
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
kernfs_link_sibling+0x555/0x850 fs/kernfs/dir.c:411
kernfs_add_one+0x1e7/0xaa0 fs/kernfs/dir.c:844
kernfs_create_dir_ns+0x157/0x2b0 fs/kernfs/dir.c:1130
sysfs_create_dir_ns+0x13a/0x2b0 fs/sysfs/dir.c:59
create_dir lib/kobject.c:73 [inline]
kobject_add_internal+0x2c8/0x930 lib/kobject.c:240
kobject_add_varg lib/kobject.c:374 [inline]
kobject_add+0x16a/0x1e0 lib/kobject.c:426
device_add+0x294/0x1970 drivers/base/core.c:3699
hid_add_device+0x2bf/0x440 drivers/hid/hid-core.c:3065
uhid_device_add_worker+0x3a/0x70 drivers/hid/uhid.c:73
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3387
process_scheduled_works kernel/workqueue.c:3470 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3551
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
input: shield Haptics as /devices/virtual/input/input5
shield 0003:0955:7214.0002: Registered Thunderstrike controller
shield 0003:0955:7214.0002: : USB HID v0.00 Gamepad [shield] on
---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [syzbot] [kernfs?] possible deadlock in kernfs_link_sibling (2)
2026-08-26 19:33 ` syzbot
@ 2026-08-26 22:49 ` Hillf Danton
2026-08-27 3:01 ` [syzbot] [net?] WARNING: locking bug in tcp_tsq_handler syzbot
2026-08-27 6:03 ` [syzbot] [kernfs?] possible deadlock in kernfs_link_sibling (2) Hillf Danton
2026-08-27 8:15 ` Hillf Danton
2 siblings, 1 reply; 8+ messages in thread
From: Hillf Danton @ 2026-08-26 22:49 UTC (permalink / raw)
To: syzbot
Cc: linux-kernel, syzkaller-bugs, syzbot+2d770620059281e225a4, Eric Dumazet
> Date: Wed, 26 Aug 2026 12:33:31 -0700 [thread overview]
> syzbot has found a reproducer for the following issue on:
>
> HEAD commit: 818bebeb63dd drm/xe: Don't hand out the flat CCS storage a..
> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> console output: https://syzkaller.appspot.com/x/log.txt?x=10059625580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=ccca94d2c01b9e78
> dashboard link: https://syzkaller.appspot.com/bug?extid=dd764a450d93885d847f
> compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13de8d49580000
#syz test
syzbot reported a lockdep splat hitting DEBUG_LOCKS_WARN_ON(1) in
hlock_class() due to an invalid class_idx:
WARNING: kernel/locking/lockdep.c:238 at __lock_acquire+0x382/0x2cf0 kernel/locking/lockdep.c:5203
Workqueue: wg-crypt-wg0 wg_packet_tx_worker
RIP: 0010:hlock_class kernel/locking/lockdep.c:238 [inline]
RIP: 0010:check_wait_context kernel/locking/lockdep.c:4870 [inline]
RIP: 0010:__lock_acquire+0x389/0x2cf0 kernel/locking/lockdep.c:5203
Call Trace:
<IRQ>
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5886
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:173
tcp_tsq_handler+0x29/0x200 net/ipv4/tcp_output.c:1291
tcp_tsq_workfn+0x384/0x410 net/ipv4/tcp_output.c:1325
...
When a lock class is zapped (e.g. during module unload or key
unregistration), zap_class() clears the class's bit in
lock_classes_in_use and removes it from the class hash table.
However, existing lockdep_map instances embedded in data structures
may still retain a pointer to the zapped class in their class_cache[]
array.
When __lock_acquire() subsequently runs on such a lock, it finds
lock->class_cache[subclass] != NULL, skipping register_lock_class() and
assigning hlock->class_idx to the index of the zapped class. When
check_wait_context() or hlock_class() inspects the held_lock, it finds
!test_bit(class_idx, lock_classes_in_use) and warns. Furthermore, if
the zapped slot is subsequently re-allocated to an unrelated lock key,
the stale class_cache entry would erroneously match the unrelated class
(ABA issue).
Add lock_class_cache_is_valid() to validate that the cached class is
within lock_classes bounds, still allocated in lock_classes_in_use
(using uninstrumented arch_test_bit() in __always_inline context so it
is safe in noinstr contexts like match_held_lock()), and that class->key
matches the expected subkey (taking lockdep_set_subclass() overrides into
account). Also use READ_ONCE()/WRITE_ONCE() when accessing class_cache[].
If the entry is invalid or stale, fall back to register_lock_class() /
look_up_lock_class().
Fixes: a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no longer in use")
Reported-by: syzbot+2d770620059281e225a4@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/6a8c66dc.4d75e56a.c9a88.0050.GAE@google.com/T/#u
Assisted-by: Gemini:gemini-3.1-pro
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
kernel/locking/lockdep.c | 50 +++++++++++++++++++++++++++++++++-------
1 file changed, 42 insertions(+), 8 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 25d77d4a1061..763f79806bd8 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -963,6 +963,34 @@ look_up_lock_class(const struct lockdep_map *lock, unsigned int subclass)
return NULL;
}
+static __always_inline bool lock_class_cache_is_valid(const struct lockdep_map *lock,
+ const struct lock_class *class,
+ unsigned int subclass)
+{
+ unsigned int class_subclass;
+
+ if (!class)
+ return false;
+
+ if (unlikely(class < lock_classes || class >= lock_classes + MAX_LOCKDEP_KEYS))
+ return false;
+
+ if (unlikely(!arch_test_bit(class - lock_classes, lock_classes_in_use)))
+ return false;
+
+ if (unlikely(!lock->key))
+ return false;
+
+ class_subclass = subclass ? subclass : class->subclass;
+ if (unlikely(class_subclass >= MAX_LOCKDEP_SUBCLASSES))
+ return false;
+
+ if (unlikely(READ_ONCE(class->key) != lock->key->subkeys + class_subclass))
+ return false;
+
+ return true;
+}
+
/*
* Static locks do not have their class-keys yet - for them the key is
* the lock object itself. If the lock is in the per cpu area, the
@@ -1395,9 +1423,9 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
out_set_class_cache:
if (!subclass || force)
- lock->class_cache[0] = class;
+ WRITE_ONCE(lock->class_cache[0], class);
else if (subclass < NR_LOCKDEP_CACHING_CLASSES)
- lock->class_cache[subclass] = class;
+ WRITE_ONCE(lock->class_cache[subclass], class);
/*
* Hash collision, did we smoke some? We found a class with a matching
@@ -4957,7 +4985,7 @@ void lockdep_init_map_type(struct lockdep_map *lock, const char *name,
int i;
for (i = 0; i < NR_LOCKDEP_CACHING_CLASSES; i++)
- lock->class_cache[i] = NULL;
+ WRITE_ONCE(lock->class_cache[i], NULL);
#ifdef CONFIG_LOCK_STAT
lock->cpu = raw_smp_processor_id();
@@ -5022,12 +5050,15 @@ EXPORT_SYMBOL_GPL(__lockdep_no_track__);
void lockdep_set_lock_cmp_fn(struct lockdep_map *lock, lock_cmp_fn cmp_fn,
lock_print_fn print_fn)
{
- struct lock_class *class = lock->class_cache[0];
+ struct lock_class *class = READ_ONCE(lock->class_cache[0]);
unsigned long flags;
raw_local_irq_save(flags);
lockdep_recursion_inc();
+ if (!lock_class_cache_is_valid(lock, class, 0))
+ class = NULL;
+
if (!class)
class = register_lock_class(lock, 0, 0);
@@ -5119,8 +5150,11 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
if (DEBUG_LOCKS_WARN_ON(subclass >= MAX_LOCKDEP_SUBCLASSES))
return 0;
- if (subclass < NR_LOCKDEP_CACHING_CLASSES)
- class = lock->class_cache[subclass];
+ if (subclass < NR_LOCKDEP_CACHING_CLASSES) {
+ class = READ_ONCE(lock->class_cache[subclass]);
+ if (!lock_class_cache_is_valid(lock, class, subclass))
+ class = NULL;
+ }
/*
* Not cached?
*/
@@ -5323,9 +5357,9 @@ static noinstr int match_held_lock(const struct held_lock *hlock,
return 1;
if (hlock->references) {
- const struct lock_class *class = lock->class_cache[0];
+ const struct lock_class *class = READ_ONCE(lock->class_cache[0]);
- if (!class)
+ if (!lock_class_cache_is_valid(lock, class, 0))
class = look_up_lock_class(lock, 0);
/*
base-commit: 0a0d1d55dad570724bf8c7ea83409639cfb4be9b
--
2.55.0.766.g2966f0265a-goog
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [syzbot] [net?] WARNING: locking bug in tcp_tsq_handler
2026-08-26 22:49 ` Hillf Danton
@ 2026-08-27 3:01 ` syzbot
0 siblings, 0 replies; 8+ messages in thread
From: syzbot @ 2026-08-27 3:01 UTC (permalink / raw)
To: edumazet, hdanton, linux-kernel, syzkaller-bugs
Hello,
syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in tcp_tsq_handler
------------[ cut here ]------------
!lockdep_sock_is_held(sk) && debug_locks
WARNING: ./include/net/sock.h:1799 at sock_owned_by_me include/net/sock.h:1799 [inline], CPU#0: kworker/0:0/9
WARNING: ./include/net/sock.h:1799 at sock_owned_by_user include/net/sock.h:1812 [inline], CPU#0: kworker/0:0/9
WARNING: ./include/net/sock.h:1799 at tcp_tsq_handler+0x1a6/0x200 net/ipv4/tcp_output.c:1292, CPU#0: kworker/0:0/9
Modules linked in:
CPU: 0 UID: 0 PID: 9 Comm: kworker/0:0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: wg-crypt-wg0 wg_packet_tx_worker
RIP: 0010:sock_owned_by_me include/net/sock.h:1799 [inline]
RIP: 0010:sock_owned_by_user include/net/sock.h:1812 [inline]
RIP: 0010:tcp_tsq_handler+0x1a6/0x200 net/ipv4/tcp_output.c:1292
Code: 00 97 96 01 e8 fb 15 79 f7 be 02 00 00 00 eb 0a e8 ef 15 79 f7 be 01 00 00 00 4c 89 ff e8 a2 7f 8e fa eb d0 e8 db 15 79 f7 90 <0f> 0b 90 e9 fd fe ff ff 44 89 f9 80 e1 07 80 c1 03 38 c1 0f 8c 07
RSP: 0018:ffffc90000007bb0 EFLAGS: 00010246
RAX: ffffffff8a4e9ad5 RBX: ffff88805ab935d0 RCX: ffff88801defddc0
RDX: 0000000000000100 RSI: 0000000000000100 RDI: 0000000000000000
RBP: 0000000000000001 R08: 0000000000000100 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff52000000f64 R12: dffffc0000000000
R13: ffffc90000007c20 R14: ffff88805ab93400 R15: ffff88805ab93400
FS: 0000000000000000(0000) GS:ffff888124ce0000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffe3b037048 CR3: 000000000eb48000 CR4: 00000000003526f0
Call Trace:
<IRQ>
tcp_tsq_workfn+0x384/0x410 net/ipv4/tcp_output.c:1325
process_one_work kernel/workqueue.c:3387 [inline]
process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3470
bh_worker+0x451/0x870 kernel/workqueue.c:3773
tasklet_action+0xc/0x70 kernel/softirq.c:997
handle_softirqs+0x226/0x860 kernel/softirq.c:645
do_softirq+0x77/0xd0 kernel/softirq.c:546
</IRQ>
<TASK>
__local_bh_enable_ip+0x100/0x140 kernel/softirq.c:473
wg_socket_send_skb_to_peer+0x16b/0x1d0 drivers/net/wireguard/socket.c:183
wg_packet_create_data_done drivers/net/wireguard/send.c:251 [inline]
wg_packet_tx_worker+0x1c8/0x7e0 drivers/net/wireguard/send.c:276
process_one_work kernel/workqueue.c:3387 [inline]
process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3470
worker_thread+0xa47/0xfb0 kernel/workqueue.c:3551
kthread+0x38b/0x480 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Tested on:
commit: 73e3f071 Merge tag 'nfs-for-7.3-1' of git://git.linux-..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15425625580000
kernel config: https://syzkaller.appspot.com/x/.config?x=22381429a4c2735a
dashboard link: https://syzkaller.appspot.com/bug?extid=2d770620059281e225a4
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
patch: https://syzkaller.appspot.com/x/patch.diff?x=10bb399e580000
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [syzbot] [kernfs?] possible deadlock in kernfs_link_sibling (2)
2026-08-26 19:33 ` syzbot
2026-08-26 22:49 ` Hillf Danton
@ 2026-08-27 6:03 ` Hillf Danton
2026-08-27 6:21 ` syzbot
2026-08-27 8:15 ` Hillf Danton
2 siblings, 1 reply; 8+ messages in thread
From: Hillf Danton @ 2026-08-27 6:03 UTC (permalink / raw)
To: syzbot; +Cc: linux-kernel, syzkaller-bugs
> Date: Wed, 26 Aug 2026 12:33:31 -0700 [thread overview]
> syzbot has found a reproducer for the following issue on:
>
> HEAD commit: 818bebeb63dd drm/xe: Don't hand out the flat CCS storage a..
> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> console output: https://syzkaller.appspot.com/x/log.txt?x=10059625580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=ccca94d2c01b9e78
> dashboard link: https://syzkaller.appspot.com/bug?extid=dd764a450d93885d847f
> compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13de8d49580000
#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 818bebeb63dd
--- x/kernel/locking/lockdep.c
+++ y/kernel/locking/lockdep.c
@@ -947,6 +947,34 @@ look_up_lock_class(const struct lockdep_
return NULL;
}
+static __always_inline bool lock_class_cache_is_valid(const struct lockdep_map *lock,
+ const struct lock_class *class,
+ unsigned int subclass)
+{
+ unsigned int class_subclass;
+
+ if (!class)
+ return false;
+
+ if (unlikely(class < lock_classes || class >= lock_classes + MAX_LOCKDEP_KEYS))
+ return false;
+
+ if (unlikely(!arch_test_bit(class - lock_classes, lock_classes_in_use)))
+ return false;
+
+ if (unlikely(!lock->key))
+ return false;
+
+ class_subclass = subclass ? subclass : class->subclass;
+ if (unlikely(class_subclass >= MAX_LOCKDEP_SUBCLASSES))
+ return false;
+
+ if (unlikely(READ_ONCE(class->key) != lock->key->subkeys + class_subclass))
+ return false;
+
+ return true;
+}
+
/*
* Static locks do not have their class-keys yet - for them the key is
* the lock object itself. If the lock is in the per cpu area, the
@@ -1379,9 +1407,9 @@ out_unlock_set:
out_set_class_cache:
if (!subclass || force)
- lock->class_cache[0] = class;
+ WRITE_ONCE(lock->class_cache[0], class);
else if (subclass < NR_LOCKDEP_CACHING_CLASSES)
- lock->class_cache[subclass] = class;
+ WRITE_ONCE(lock->class_cache[subclass], class);
/*
* Hash collision, did we smoke some? We found a class with a matching
@@ -4941,7 +4969,7 @@ void lockdep_init_map_type(struct lockde
int i;
for (i = 0; i < NR_LOCKDEP_CACHING_CLASSES; i++)
- lock->class_cache[i] = NULL;
+ WRITE_ONCE(lock->class_cache[i], NULL);
#ifdef CONFIG_LOCK_STAT
lock->cpu = raw_smp_processor_id();
@@ -5006,12 +5034,15 @@ EXPORT_SYMBOL_GPL(__lockdep_no_track__);
void lockdep_set_lock_cmp_fn(struct lockdep_map *lock, lock_cmp_fn cmp_fn,
lock_print_fn print_fn)
{
- struct lock_class *class = lock->class_cache[0];
+ struct lock_class *class = READ_ONCE(lock->class_cache[0]);
unsigned long flags;
raw_local_irq_save(flags);
lockdep_recursion_inc();
+ if (!lock_class_cache_is_valid(lock, class, 0))
+ class = NULL;
+
if (!class)
class = register_lock_class(lock, 0, 0);
@@ -5103,8 +5134,11 @@ static int __lock_acquire(struct lockdep
if (DEBUG_LOCKS_WARN_ON(subclass >= MAX_LOCKDEP_SUBCLASSES))
return 0;
- if (subclass < NR_LOCKDEP_CACHING_CLASSES)
- class = lock->class_cache[subclass];
+ if (subclass < NR_LOCKDEP_CACHING_CLASSES) {
+ class = READ_ONCE(lock->class_cache[subclass]);
+ if (!lock_class_cache_is_valid(lock, class, subclass))
+ class = NULL;
+ }
/*
* Not cached?
*/
@@ -5307,9 +5341,9 @@ static noinstr int match_held_lock(const
return 1;
if (hlock->references) {
- const struct lock_class *class = lock->class_cache[0];
+ const struct lock_class *class = READ_ONCE(lock->class_cache[0]);
- if (!class)
+ if (!lock_class_cache_is_valid(lock, class, 0))
class = look_up_lock_class(lock, 0);
/*
--- x/lib/once.c
+++ y/lib/once.c
@@ -93,6 +93,6 @@ void __do_once_sleepable_done(bool *done
{
*done = true;
mutex_unlock(&once_mutex);
- static_branch_disable(once_key);
+ once_disable_jump(once_key, mod);
}
EXPORT_SYMBOL(__do_once_sleepable_done);
--
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [syzbot] [kernfs?] possible deadlock in kernfs_link_sibling (2)
2026-08-27 6:03 ` [syzbot] [kernfs?] possible deadlock in kernfs_link_sibling (2) Hillf Danton
@ 2026-08-27 6:21 ` syzbot
0 siblings, 0 replies; 8+ messages in thread
From: syzbot @ 2026-08-27 6:21 UTC (permalink / raw)
To: hdanton, linux-kernel, syzkaller-bugs
Hello,
syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in kernfs_link_sibling
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
kworker/0:4/5891 is trying to acquire lock:
ffff88801d6a5a10 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_link_sibling+0x555/0x850 fs/kernfs/dir.c:411
but task is already holding lock:
ffff88801d6a5980 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_add_one+0x38/0xaa0 fs/kernfs/dir.c:825
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #9 (&root->kernfs_rwsem){++++}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5920 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5877
down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
kernfs_add_one+0x38/0xaa0 fs/kernfs/dir.c:825
kernfs_create_dir_ns+0x157/0x2b0 fs/kernfs/dir.c:1130
internal_create_group+0x36f/0xfb0 fs/sysfs/group.c:176
cpuhp_invoke_callback+0x3b4/0x9a0 kernel/cpu.c:194
cpuhp_issue_call+0x1b8/0x970 kernel/cpu.c:2354
__cpuhp_setup_state_cpuslocked+0x431/0x880 kernel/cpu.c:2507
__cpuhp_setup_state+0xf7/0x2f0 kernel/cpu.c:2536
do_one_initcall+0x11c/0x6f0 init/main.c:1353
do_initcall_level init/main.c:1415 [inline]
do_initcalls init/main.c:1431 [inline]
do_basic_setup init/main.c:1451 [inline]
kernel_init_freeable+0x6ea/0x7b0 init/main.c:1666
kernel_init+0x21/0x1e0 init/main.c:1556
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #8 (cpuhp_state_mutex){+.+.}-{4:4}:
-> #7 (cpu_hotplug_lock){++++}-{0:0}:
lock_acquire kernel/locking/lockdep.c:5920 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5877
percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
cpus_read_lock+0x42/0x170 kernel/cpu.c:490
static_key_slow_inc+0x12/0x30 kernel/jump_label.c:190
nbd_genl_reconnect_sock_cb+0x39f/0x990 drivers/block/nbd.c:1377
nbd_genl_foreach_sock+0x2ab/0x3e0 drivers/block/nbd.c:2152
nbd_genl_reconfigure+0x861/0xde0 drivers/block/nbd.c:2477
genl_family_rcv_msg_doit+0x214/0x300 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x560/0x800 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2556
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1900
sock_sendmsg_nosec net/socket.c:800 [inline]
__sock_sendmsg net/socket.c:815 [inline]
__sys_sendto+0x48b/0x4e0 net/socket.c:2281
__do_sys_sendto net/socket.c:2288 [inline]
__se_sys_sendto net/socket.c:2284 [inline]
__x64_sys_sendto+0xe0/0x1c0 net/socket.c:2284
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #6 (&nsock->tx_lock){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5920 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5877
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821
nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
nbd_queue_rq+0x42d/0xfa0 drivers/block/nbd.c:1207
blk_mq_dispatch_rq_list+0x428/0x1e60 block/blk-mq.c:2117
__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+0xcea/0x1620 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
blk_mq_run_work_fn+0x135/0x380 block/blk-mq.c:2531
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3387
process_scheduled_works kernel/workqueue.c:3470 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3551
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #5 (&cmd->lock){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5920 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5877
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821
nbd_queue_rq+0xba/0xfa0 drivers/block/nbd.c:1199
blk_mq_dispatch_rq_list+0x428/0x1e60 block/blk-mq.c:2117
__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+0xcea/0x1620 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
blk_mq_run_work_fn+0x135/0x380 block/blk-mq.c:2531
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3387
process_scheduled_works kernel/workqueue.c:3470 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3551
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #4 (set->srcu){.+.+}-{0:0}:
lock_sync kernel/locking/lockdep.c:5968 [inline]
lock_sync+0x9d/0x110 kernel/locking/lockdep.c:5956
srcu_lock_sync include/linux/srcu.h:199 [inline]
__synchronize_srcu+0xa2/0x300 kernel/rcu/srcutree.c:1481
blk_mq_wait_quiesce_done block/blk-mq.c:284 [inline]
blk_mq_wait_quiesce_done block/blk-mq.c:281 [inline]
blk_mq_quiesce_queue block/blk-mq.c:304 [inline]
blk_mq_quiesce_queue+0x149/0x1c0 block/blk-mq.c:299
elevator_switch+0x17b/0x7e0 block/elevator.c:576
elevator_change+0x352/0x530 block/elevator.c:681
elevator_set_default+0x29e/0x360 block/elevator.c:754
blk_register_queue+0x48e/0x630 block/blk-sysfs.c:992
__add_disk+0x73f/0xe40 block/genhd.c:524
add_disk_fwnode+0x118/0x480 block/genhd.c:593
add_disk include/linux/blkdev.h:798 [inline]
nbd_dev_add+0x779/0xb10 drivers/block/nbd.c:2026
nbd_init+0x2c5/0x2e0 drivers/block/nbd.c:2743
do_one_initcall+0x11c/0x6f0 init/main.c:1353
do_initcall_level init/main.c:1415 [inline]
do_initcalls init/main.c:1431 [inline]
do_basic_setup init/main.c:1451 [inline]
kernel_init_freeable+0x6ea/0x7b0 init/main.c:1666
kernel_init+0x21/0x1e0 init/main.c:1556
ret_from_fork+0x730/0xd60 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}:
lock_acquire kernel/locking/lockdep.c:5920 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5877
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821
elevator_change+0x1bc/0x530 block/elevator.c:679
elevator_set_none+0x92/0xf0 block/elevator.c:769
blk_mq_elv_switch_none block/blk-mq.c:5102 [inline]
__blk_mq_update_nr_hw_queues block/blk-mq.c:5147 [inline]
blk_mq_update_nr_hw_queues+0x4c1/0x15f0 block/blk-mq.c:5212
nbd_start_device+0x1a6/0xbd0 drivers/block/nbd.c:1530
nbd_genl_connect+0xfc2/0x1760 drivers/block/nbd.c:2310
genl_family_rcv_msg_doit+0x214/0x300 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x560/0x800 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2556
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1900
sock_sendmsg_nosec net/socket.c:800 [inline]
__sock_sendmsg net/socket.c:815 [inline]
__sys_sendto+0x48b/0x4e0 net/socket.c:2281
__do_sys_sendto net/socket.c:2288 [inline]
__se_sys_sendto net/socket.c:2284 [inline]
__x64_sys_sendto+0xe0/0x1c0 net/socket.c:2284
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #2 (&q->q_usage_counter(io)#49){++++}-{0:0}:
lock_acquire kernel/locking/lockdep.c:5920 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5877
blk_alloc_queue+0x610/0x790 block/blk-core.c:504
blk_mq_alloc_queue+0x174/0x290 block/blk-mq.c:4420
__blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4467
nbd_dev_add+0x491/0xb10 drivers/block/nbd.c:1996
nbd_init+0x2c5/0x2e0 drivers/block/nbd.c:2743
do_one_initcall+0x11c/0x6f0 init/main.c:1353
do_initcall_level init/main.c:1415 [inline]
do_initcalls init/main.c:1431 [inline]
do_basic_setup init/main.c:1451 [inline]
kernel_init_freeable+0x6ea/0x7b0 init/main.c:1666
kernel_init+0x21/0x1e0 init/main.c:1556
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #1 (fs_reclaim){+.+.}-{0:0}:
lock_acquire kernel/locking/lockdep.c:5920 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5877
__fs_reclaim_acquire mm/page_alloc.c:4375 [inline]
fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4389
might_alloc include/linux/sched/mm.h:314 [inline]
slab_pre_alloc_hook mm/slub.c:4539 [inline]
slab_alloc_node mm/slub.c:4899 [inline]
kmem_cache_alloc_noprof+0x63/0x6a0 mm/slub.c:4933
__kernfs_iattrs+0x126/0x450 fs/kernfs/inode.c:36
kernfs_iattrs fs/kernfs/inode.c:60 [inline]
__kernfs_setattr+0x4d/0x3c0 fs/kernfs/inode.c:73
kernfs_iop_setattr+0xda/0x130 fs/kernfs/inode.c:127
notify_change+0xb25/0x1330 fs/attr.c:556
do_truncate+0x1df/0x240 fs/open.c:68
handle_truncate fs/namei.c:4300 [inline]
do_open fs/namei.c:4841 [inline]
path_openat+0x1e6d/0x2440 fs/namei.c:5000
do_file_open+0x20e/0x430 fs/namei.c:5029
do_sys_openat2+0x10f/0x1e0 fs/open.c:1417
do_sys_open fs/open.c:1423 [inline]
__do_sys_openat fs/open.c:1439 [inline]
__se_sys_openat fs/open.c:1434 [inline]
__x64_sys_openat+0x12d/0x210 fs/open.c:1434
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #0 (&root->kernfs_iattr_rwsem){++++}-{4:4}:
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x1508/0x1f20 kernel/locking/lockdep.c:5287
lock_acquire kernel/locking/lockdep.c:5920 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5877
down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
kernfs_link_sibling+0x555/0x850 fs/kernfs/dir.c:411
kernfs_add_one+0x1e7/0xaa0 fs/kernfs/dir.c:844
kernfs_create_dir_ns+0x157/0x2b0 fs/kernfs/dir.c:1130
sysfs_create_dir_ns+0x13a/0x2b0 fs/sysfs/dir.c:59
create_dir lib/kobject.c:73 [inline]
kobject_add_internal+0x2c8/0x930 lib/kobject.c:240
kobject_add_varg lib/kobject.c:374 [inline]
kobject_add+0x16a/0x1e0 lib/kobject.c:426
device_add+0x294/0x1970 drivers/base/core.c:3699
hid_add_device+0x2bf/0x440 drivers/hid/hid-core.c:3065
uhid_device_add_worker+0x3a/0x70 drivers/hid/uhid.c:73
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3387
process_scheduled_works kernel/workqueue.c:3470 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3551
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
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 ***
locks held by kworker/0:4/5891: 3, last CPU#0:
#0: ffff88801c0aa940 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x1466/0x1b10 kernel/workqueue.c:3362
#1: ffffc90003487d08 ((work_completion)(&uhid->worker)){+.+.}-{0:0}, at: process_one_work+0xa2c/0x1b10 kernel/workqueue.c:3363
#2: ffff88801d6a5980 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_add_one+0x38/0xaa0 fs/kernfs/dir.c:825
stack backtrace:
CPU: 0 UID: 0 PID: 5891 Comm: kworker/0:4 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Workqueue: events uhid_device_add_worker
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
print_circular_bug.cold+0x178/0x1be kernel/locking/lockdep.c:2087
check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2219
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3209
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x1508/0x1f20 kernel/locking/lockdep.c:5287
lock_acquire kernel/locking/lockdep.c:5920 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5877
down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
kernfs_link_sibling+0x555/0x850 fs/kernfs/dir.c:411
kernfs_add_one+0x1e7/0xaa0 fs/kernfs/dir.c:844
kernfs_create_dir_ns+0x157/0x2b0 fs/kernfs/dir.c:1130
sysfs_create_dir_ns+0x13a/0x2b0 fs/sysfs/dir.c:59
create_dir lib/kobject.c:73 [inline]
kobject_add_internal+0x2c8/0x930 lib/kobject.c:240
kobject_add_varg lib/kobject.c:374 [inline]
kobject_add+0x16a/0x1e0 lib/kobject.c:426
device_add+0x294/0x1970 drivers/base/core.c:3699
hid_add_device+0x2bf/0x440 drivers/hid/hid-core.c:3065
uhid_device_add_worker+0x3a/0x70 drivers/hid/uhid.c:73
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3387
process_scheduled_works kernel/workqueue.c:3470 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3551
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
input: shield Haptics as /devices/virtual/input/input5
shield 0003:0955:7214.0002: Registered Thunderstrike controller
shield 0003:0955:7214.0002: : USB HID v0.00 Gamepad [shield] on
Tested on:
commit: 818bebeb drm/xe: Don't hand out the flat CCS storage a..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=159e6d49580000
kernel config: https://syzkaller.appspot.com/x/.config?x=ccca94d2c01b9e78
dashboard link: https://syzkaller.appspot.com/bug?extid=dd764a450d93885d847f
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
patch: https://syzkaller.appspot.com/x/patch.diff?x=111eb415580000
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [syzbot] [kernfs?] possible deadlock in kernfs_link_sibling (2)
2026-08-26 19:33 ` syzbot
2026-08-26 22:49 ` Hillf Danton
2026-08-27 6:03 ` [syzbot] [kernfs?] possible deadlock in kernfs_link_sibling (2) Hillf Danton
@ 2026-08-27 8:15 ` Hillf Danton
2026-08-27 10:33 ` syzbot
2 siblings, 1 reply; 8+ messages in thread
From: Hillf Danton @ 2026-08-27 8:15 UTC (permalink / raw)
To: syzbot; +Cc: linux-kernel, syzkaller-bugs
> Date: Wed, 26 Aug 2026 12:33:31 -0700 [thread overview]
> syzbot has found a reproducer for the following issue on:
>
> HEAD commit: 818bebeb63dd drm/xe: Don't hand out the flat CCS storage a..
> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> console output: https://syzkaller.appspot.com/x/log.txt?x=10059625580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=ccca94d2c01b9e78
> dashboard link: https://syzkaller.appspot.com/bug?extid=dd764a450d93885d847f
> compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13de8d49580000
#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 818bebeb63dd
--- x/lib/once.c
+++ y/lib/once.c
@@ -93,6 +93,6 @@ void __do_once_sleepable_done(bool *done
{
*done = true;
mutex_unlock(&once_mutex);
- static_branch_disable(once_key);
+ once_disable_jump(once_key, mod);
}
EXPORT_SYMBOL(__do_once_sleepable_done);
--
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [syzbot] [kernfs?] possible deadlock in kernfs_link_sibling (2)
2026-08-27 8:15 ` Hillf Danton
@ 2026-08-27 10:33 ` syzbot
0 siblings, 0 replies; 8+ messages in thread
From: syzbot @ 2026-08-27 10:33 UTC (permalink / raw)
To: hdanton, linux-kernel, syzkaller-bugs
Hello,
syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in kernfs_link_sibling
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
kworker/2:1/50 is trying to acquire lock:
ffff88801d6a5a10 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_link_sibling+0x555/0x850 fs/kernfs/dir.c:411
but task is already holding lock:
ffff88801d6a5980 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_add_one+0x38/0xaa0 fs/kernfs/dir.c:825
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #9 (&root->kernfs_rwsem){++++}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
kernfs_add_one+0x38/0xaa0 fs/kernfs/dir.c:825
kernfs_create_dir_ns+0x157/0x2b0 fs/kernfs/dir.c:1130
internal_create_group+0x36f/0xfb0 fs/sysfs/group.c:176
cpuhp_invoke_callback+0x3b4/0x9a0 kernel/cpu.c:194
cpuhp_issue_call+0x1b8/0x970 kernel/cpu.c:2354
__cpuhp_setup_state_cpuslocked+0x431/0x880 kernel/cpu.c:2507
__cpuhp_setup_state+0xf7/0x2f0 kernel/cpu.c:2536
do_one_initcall+0x11c/0x6f0 init/main.c:1353
do_initcall_level init/main.c:1415 [inline]
do_initcalls init/main.c:1431 [inline]
do_basic_setup init/main.c:1451 [inline]
kernel_init_freeable+0x6ea/0x7b0 init/main.c:1666
kernel_init+0x21/0x1e0 init/main.c:1556
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #8 (cpuhp_state_mutex){+.+.}-{4:4}:
-> #7 (cpu_hotplug_lock){++++}-{0:0}:
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
cpus_read_lock+0x42/0x170 kernel/cpu.c:490
static_key_slow_inc+0x12/0x30 kernel/jump_label.c:190
nbd_genl_reconnect_sock_cb+0x39f/0x990 drivers/block/nbd.c:1377
nbd_genl_foreach_sock+0x2ab/0x3e0 drivers/block/nbd.c:2152
nbd_genl_reconfigure+0x861/0xde0 drivers/block/nbd.c:2477
genl_family_rcv_msg_doit+0x214/0x300 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x560/0x800 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2556
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1900
sock_sendmsg_nosec net/socket.c:800 [inline]
__sock_sendmsg net/socket.c:815 [inline]
__sys_sendto+0x48b/0x4e0 net/socket.c:2281
__do_sys_sendto net/socket.c:2288 [inline]
__se_sys_sendto net/socket.c:2284 [inline]
__x64_sys_sendto+0xe0/0x1c0 net/socket.c:2284
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #6 (&nsock->tx_lock){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821
nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
nbd_queue_rq+0x42d/0xfa0 drivers/block/nbd.c:1207
blk_mq_dispatch_rq_list+0x428/0x1e60 block/blk-mq.c:2117
__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+0xcea/0x1620 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
blk_mq_run_work_fn+0x135/0x380 block/blk-mq.c:2531
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3387
process_scheduled_works kernel/workqueue.c:3470 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3551
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #5 (&cmd->lock){+.+.}-{4:4}:
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821
nbd_queue_rq+0xba/0xfa0 drivers/block/nbd.c:1199
blk_mq_dispatch_rq_list+0x428/0x1e60 block/blk-mq.c:2117
__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+0xcea/0x1620 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xd7/0x1c0 block/blk-mq-sched.c:329
blk_mq_run_work_fn+0x135/0x380 block/blk-mq.c:2531
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3387
process_scheduled_works kernel/workqueue.c:3470 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3551
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #4 (set->srcu){.+.+}-{0:0}:
lock_sync kernel/locking/lockdep.c:5934 [inline]
lock_sync+0x9d/0x110 kernel/locking/lockdep.c:5922
srcu_lock_sync include/linux/srcu.h:199 [inline]
__synchronize_srcu+0xa2/0x300 kernel/rcu/srcutree.c:1481
blk_mq_wait_quiesce_done block/blk-mq.c:284 [inline]
blk_mq_wait_quiesce_done block/blk-mq.c:281 [inline]
blk_mq_quiesce_queue block/blk-mq.c:304 [inline]
blk_mq_quiesce_queue+0x149/0x1c0 block/blk-mq.c:299
elevator_switch+0x17b/0x7e0 block/elevator.c:576
elevator_change+0x352/0x530 block/elevator.c:681
elevator_set_default+0x29e/0x360 block/elevator.c:754
blk_register_queue+0x48e/0x630 block/blk-sysfs.c:992
__add_disk+0x73f/0xe40 block/genhd.c:524
add_disk_fwnode+0x118/0x480 block/genhd.c:593
add_disk include/linux/blkdev.h:798 [inline]
nbd_dev_add+0x779/0xb10 drivers/block/nbd.c:2026
nbd_init+0x2c5/0x2e0 drivers/block/nbd.c:2743
do_one_initcall+0x11c/0x6f0 init/main.c:1353
do_initcall_level init/main.c:1415 [inline]
do_initcalls init/main.c:1431 [inline]
do_basic_setup init/main.c:1451 [inline]
kernel_init_freeable+0x6ea/0x7b0 init/main.c:1666
kernel_init+0x21/0x1e0 init/main.c:1556
ret_from_fork+0x730/0xd60 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}:
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x1a4/0x1bc0 kernel/locking/mutex.c:821
elevator_change+0x1bc/0x530 block/elevator.c:679
elevator_set_none+0x92/0xf0 block/elevator.c:769
blk_mq_elv_switch_none block/blk-mq.c:5102 [inline]
__blk_mq_update_nr_hw_queues block/blk-mq.c:5147 [inline]
blk_mq_update_nr_hw_queues+0x4c1/0x15f0 block/blk-mq.c:5212
nbd_start_device+0x1a6/0xbd0 drivers/block/nbd.c:1530
nbd_genl_connect+0xfc2/0x1760 drivers/block/nbd.c:2310
genl_family_rcv_msg_doit+0x214/0x300 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x560/0x800 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2556
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1900
sock_sendmsg_nosec net/socket.c:800 [inline]
__sock_sendmsg net/socket.c:815 [inline]
__sys_sendto+0x48b/0x4e0 net/socket.c:2281
__do_sys_sendto net/socket.c:2288 [inline]
__se_sys_sendto net/socket.c:2284 [inline]
__x64_sys_sendto+0xe0/0x1c0 net/socket.c:2284
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #2 (&q->q_usage_counter(io)#49){++++}-{0:0}:
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
blk_alloc_queue+0x610/0x790 block/blk-core.c:504
blk_mq_alloc_queue+0x174/0x290 block/blk-mq.c:4420
__blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4467
nbd_dev_add+0x491/0xb10 drivers/block/nbd.c:1996
nbd_init+0x2c5/0x2e0 drivers/block/nbd.c:2743
do_one_initcall+0x11c/0x6f0 init/main.c:1353
do_initcall_level init/main.c:1415 [inline]
do_initcalls init/main.c:1431 [inline]
do_basic_setup init/main.c:1451 [inline]
kernel_init_freeable+0x6ea/0x7b0 init/main.c:1666
kernel_init+0x21/0x1e0 init/main.c:1556
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
-> #1 (fs_reclaim){+.+.}-{0:0}:
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
__fs_reclaim_acquire mm/page_alloc.c:4375 [inline]
fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4389
might_alloc include/linux/sched/mm.h:314 [inline]
slab_pre_alloc_hook mm/slub.c:4539 [inline]
slab_alloc_node mm/slub.c:4899 [inline]
kmem_cache_alloc_noprof+0x63/0x6a0 mm/slub.c:4933
__kernfs_iattrs+0x126/0x450 fs/kernfs/inode.c:36
kernfs_iattrs fs/kernfs/inode.c:60 [inline]
__kernfs_setattr+0x4d/0x3c0 fs/kernfs/inode.c:73
kernfs_iop_setattr+0xda/0x130 fs/kernfs/inode.c:127
notify_change+0xb25/0x1330 fs/attr.c:556
do_truncate+0x1df/0x240 fs/open.c:68
handle_truncate fs/namei.c:4300 [inline]
do_open fs/namei.c:4841 [inline]
path_openat+0x1e6d/0x2440 fs/namei.c:5000
do_file_open+0x20e/0x430 fs/namei.c:5029
do_sys_openat2+0x10f/0x1e0 fs/open.c:1417
do_sys_open fs/open.c:1423 [inline]
__do_sys_openat fs/open.c:1439 [inline]
__se_sys_openat fs/open.c:1434 [inline]
__x64_sys_openat+0x12d/0x210 fs/open.c:1434
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #0 (&root->kernfs_iattr_rwsem){++++}-{4:4}:
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3181
check_prevs_add kernel/locking/lockdep.c:3300 [inline]
validate_chain kernel/locking/lockdep.c:3924 [inline]
__lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5253
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
kernfs_link_sibling+0x555/0x850 fs/kernfs/dir.c:411
kernfs_add_one+0x1e7/0xaa0 fs/kernfs/dir.c:844
kernfs_create_dir_ns+0x157/0x2b0 fs/kernfs/dir.c:1130
sysfs_create_dir_ns+0x13a/0x2b0 fs/sysfs/dir.c:59
create_dir lib/kobject.c:73 [inline]
kobject_add_internal+0x2c8/0x930 lib/kobject.c:240
kobject_add_varg lib/kobject.c:374 [inline]
kobject_add+0x16a/0x1e0 lib/kobject.c:426
device_add+0x294/0x1970 drivers/base/core.c:3699
hid_add_device+0x2bf/0x440 drivers/hid/hid-core.c:3065
uhid_device_add_worker+0x3a/0x70 drivers/hid/uhid.c:73
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3387
process_scheduled_works kernel/workqueue.c:3470 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3551
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
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 ***
locks held by kworker/2:1/50: 3, last CPU#2:
#0: ffff88801c0aa940 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x1466/0x1b10 kernel/workqueue.c:3362
#1: ffffc90000a3fd08 ((work_completion)(&uhid->worker)){+.+.}-{0:0}, at: process_one_work+0xa2c/0x1b10 kernel/workqueue.c:3363
#2: ffff88801d6a5980 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_add_one+0x38/0xaa0 fs/kernfs/dir.c:825
stack backtrace:
CPU: 2 UID: 0 PID: 50 Comm: kworker/2:1 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Workqueue: events uhid_device_add_worker
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
print_circular_bug.cold+0x178/0x1be kernel/locking/lockdep.c:2059
check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2191
check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3181
check_prevs_add kernel/locking/lockdep.c:3300 [inline]
validate_chain kernel/locking/lockdep.c:3924 [inline]
__lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5253
lock_acquire kernel/locking/lockdep.c:5886 [inline]
lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5843
down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631
kernfs_link_sibling+0x555/0x850 fs/kernfs/dir.c:411
kernfs_add_one+0x1e7/0xaa0 fs/kernfs/dir.c:844
kernfs_create_dir_ns+0x157/0x2b0 fs/kernfs/dir.c:1130
sysfs_create_dir_ns+0x13a/0x2b0 fs/sysfs/dir.c:59
create_dir lib/kobject.c:73 [inline]
kobject_add_internal+0x2c8/0x930 lib/kobject.c:240
kobject_add_varg lib/kobject.c:374 [inline]
kobject_add+0x16a/0x1e0 lib/kobject.c:426
device_add+0x294/0x1970 drivers/base/core.c:3699
hid_add_device+0x2bf/0x440 drivers/hid/hid-core.c:3065
uhid_device_add_worker+0x3a/0x70 drivers/hid/uhid.c:73
process_one_work+0xac7/0x1b10 kernel/workqueue.c:3387
process_scheduled_works kernel/workqueue.c:3470 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3551
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
input: shield Haptics as /devices/virtual/input/input5
shield 0003:0955:7214.0002: Registered Thunderstrike controller
shield 0003:0955:7214.0002: : USB HID v0.00 Gamepad [shield] on
Tested on:
commit: 818bebeb drm/xe: Don't hand out the flat CCS storage a..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=166f5625580000
kernel config: https://syzkaller.appspot.com/x/.config?x=ccca94d2c01b9e78
dashboard link: https://syzkaller.appspot.com/bug?extid=dd764a450d93885d847f
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
patch: https://syzkaller.appspot.com/x/patch.diff?x=128f6579580000
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2026-08-27 10:33 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2026-03-17 17:33 [syzbot] [kernfs?] possible deadlock in kernfs_link_sibling (2) syzbot
2026-08-26 19:33 ` syzbot
2026-08-26 22:49 ` Hillf Danton
2026-08-27 3:01 ` [syzbot] [net?] WARNING: locking bug in tcp_tsq_handler syzbot
2026-08-27 6:03 ` [syzbot] [kernfs?] possible deadlock in kernfs_link_sibling (2) Hillf Danton
2026-08-27 6:21 ` syzbot
2026-08-27 8:15 ` Hillf Danton
2026-08-27 10:33 ` syzbot
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox
all inboxes | Powered by JetHome®