* [syzbot] [driver-core?] possible deadlock in device_register (2)
@ 2026-10-27 14:19 syzbot
0 siblings, 0 replies; only message in thread
From: syzbot @ 2026-10-27 14:19 UTC (permalink / raw)
To: dakr, driver-core, linux-kernel, syzkaller-bugs
Hello,
syzbot found the following issue on:
HEAD commit: 7a19f0cc94ad Merge branch 'for-next/core' into for-kernelci
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=17ba5fc9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6602d83d2f34eb80
dashboard link: https://syzkaller.appspot.com/bug?extid=a246ab421a728c78b4ad
compiler: Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
userspace arch: arm64
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10b04a95580000
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a246ab421a728c78b4ad@syzkaller.appspotmail.com
block nbd0: reconnected socket
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz-executor796/5066 is trying to acquire lock:
ffff800089aea6a0 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:316 [inline]
ffff800089aea6a0 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4636 [inline]
ffff800089aea6a0 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:4974 [inline]
ffff800089aea6a0 (fs_reclaim){+.+.}-{0:0}, at: kmem_cache_alloc_node_noprof+0x64/0x604 mm/slub.c:5068
but task is already holding lock:
ffff80008ae5fb20 (uevent_sock_mutex){+.+.}-{4:4}, at: uevent_net_broadcast_untagged lib/kobject_uevent.c:317 [inline]
ffff80008ae5fb20 (uevent_sock_mutex){+.+.}-{4:4}, at: kobject_uevent_net_broadcast+0x24c/0x53c lib/kobject_uevent.c:410
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #7 (uevent_sock_mutex){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x164/0x1078 kernel/locking/mutex.c:821
mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874
uevent_net_broadcast_untagged lib/kobject_uevent.c:317 [inline]
kobject_uevent_net_broadcast+0x24c/0x53c lib/kobject_uevent.c:410
kobject_uevent_env+0x518/0x944 lib/kobject_uevent.c:611
kobject_uevent+0x2c/0x3c lib/kobject_uevent.c:659
device_add+0x4d0/0x9e0 drivers/base/core.c:3742
device_register+0x28/0x38 drivers/base/core.c:3858
register_cpu+0x28c/0x57c drivers/base/cpu.c:431
arch_register_cpu+0x160/0x224 arch/arm64/kernel/smp.c:535
acpi_processor_hotadd_init drivers/acpi/acpi_processor.c:248 [inline]
acpi_processor_get_info drivers/acpi/acpi_processor.c:370 [inline]
acpi_processor_add+0x8f0/0x13f0 drivers/acpi/acpi_processor.c:441
acpi_scan_attach_handler drivers/acpi/scan.c:2325 [inline]
acpi_bus_attach+0x398/0x778 drivers/acpi/scan.c:2374
acpi_dev_for_one_check+0xa0/0xb4 drivers/acpi/bus.c:1172
device_for_each_child+0xf4/0x184 drivers/base/core.c:4105
acpi_dev_for_each_child+0x98/0xe4 drivers/acpi/bus.c:1184
acpi_bus_attach+0x540/0x778 drivers/acpi/scan.c:2390
acpi_dev_for_one_check+0xa0/0xb4 drivers/acpi/bus.c:1172
device_for_each_child+0xf4/0x184 drivers/base/core.c:4105
acpi_dev_for_each_child+0x98/0xe4 drivers/acpi/bus.c:1184
acpi_bus_attach+0x540/0x778 drivers/acpi/scan.c:2390
acpi_bus_scan+0x104/0x310 drivers/acpi/scan.c:2740
acpi_scan_init+0x168/0x3cc drivers/acpi/scan.c:2866
acpi_init+0x15c/0x1f4 drivers/acpi/bus.c:1499
do_one_initcall+0x274/0x9f8 init/main.c:1362
do_initcall_level+0x12c/0x1c4 init/main.c:1424
do_initcalls+0x70/0xd0 init/main.c:1440
do_basic_setup+0x7c/0x90 init/main.c:1460
kernel_init_freeable+0x258/0x398 init/main.c:1675
kernel_init+0x28/0x1e0 init/main.c:1565
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:854
-> #6 (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+0x54/0x1c8 kernel/cpu.c:490
static_key_slow_inc+0x1c/0x40 kernel/jump_label.c:190
sk_set_memalloc+0x6c/0xa0 net/core/sock.c:307
nbd_genl_reconnect_sock_cb+0x32c/0x72c drivers/block/nbd.c:1377
nbd_genl_foreach_sock+0x204/0x3c8 drivers/block/nbd.c:2152
nbd_genl_reconfigure+0x714/0x9e8 drivers/block/nbd.c:2477
genl_family_rcv_msg_doit+0x1e4/0x2d4 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x43c/0x620 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x238/0x414 net/netlink/af_netlink.c:2575
genl_rcv+0x38/0x50 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1338 [inline]
netlink_unicast+0x600/0x7f8 net/netlink/af_netlink.c:1364
netlink_sendmsg+0x648/0x948 net/netlink/af_netlink.c:1919
sock_sendmsg_nosec net/socket.c:800 [inline]
__sock_sendmsg+0xc8/0x17c net/socket.c:815
__sys_sendto+0x250/0x328 net/socket.c:2281
__do_sys_sendto net/socket.c:2288 [inline]
__se_sys_sendto net/socket.c:2284 [inline]
__arm64_sys_sendto+0xec/0x10c net/socket.c:2284
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
el0_svc+0x60/0x1d8 arch/arm64/kernel/entry-common.c:796
el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:815
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:606
-> #5 (&nsock->tx_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x164/0x1078 kernel/locking/mutex.c:821
mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874
nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
nbd_queue_rq+0x1f4/0xbac drivers/block/nbd.c:1207
blk_mq_dispatch_rq_list+0x3d4/0x13a8 block/blk-mq.c:2130
__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+0xa48/0x10e8 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xa8/0x158 block/blk-mq-sched.c:329
blk_mq_run_work_fn+0x154/0x2e4 block/blk-mq.c:2545
process_one_work kernel/workqueue.c:3396 [inline]
process_scheduled_works+0x91c/0x1250 kernel/workqueue.c:3479
worker_thread+0x798/0xbd0 kernel/workqueue.c:3560
kthread+0x304/0x3d4 kernel/kthread.c:436
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:854
-> #4 (&cmd->lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x164/0x1078 kernel/locking/mutex.c:821
mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874
nbd_queue_rq+0xb0/0xbac drivers/block/nbd.c:1199
blk_mq_dispatch_rq_list+0x3d4/0x13a8 block/blk-mq.c:2130
__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+0xa48/0x10e8 block/blk-mq-sched.c:307
blk_mq_sched_dispatch_requests+0xa8/0x158 block/blk-mq-sched.c:329
blk_mq_run_work_fn+0x154/0x2e4 block/blk-mq.c:2545
process_one_work kernel/workqueue.c:3396 [inline]
process_scheduled_works+0x91c/0x1250 kernel/workqueue.c:3479
worker_thread+0x798/0xbd0 kernel/workqueue.c:3560
kthread+0x304/0x3d4 kernel/kthread.c:436
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:854
-> #3 (set->srcu){.+.+}-{0:0}:
srcu_lock_sync include/linux/srcu.h:210 [inline]
__synchronize_srcu+0xc8/0x268 kernel/rcu/srcutree.c:1462
synchronize_srcu+0x280/0x2e0 kernel/rcu/srcutree.c:-1
blk_mq_wait_quiesce_done+0x88/0xac block/blk-mq.c:284
blk_mq_quiesce_queue+0x70/0x8c block/blk-mq.c:304
elevator_switch+0x128/0x38c block/elevator.c:576
elevator_change+0x204/0x35c block/elevator.c:681
elevator_set_default+0x190/0x2b0 block/elevator.c:754
blk_register_queue+0x304/0x3dc block/blk-sysfs.c:992
__add_disk+0x5c8/0xbdc block/genhd.c:531
add_disk_fwnode+0xd4/0x340 block/genhd.c:600
device_add_disk+0x38/0x4c block/genhd.c:630
add_disk include/linux/blkdev.h:798 [inline]
nbd_dev_add+0x594/0x884 drivers/block/nbd.c:2026
nbd_init+0x174/0x19c drivers/block/nbd.c:2743
do_one_initcall+0x274/0x9f8 init/main.c:1362
do_initcall_level+0x12c/0x1c4 init/main.c:1424
do_initcalls+0x70/0xd0 init/main.c:1440
do_basic_setup+0x7c/0x90 init/main.c:1460
kernel_init_freeable+0x258/0x398 init/main.c:1675
kernel_init+0x28/0x1e0 init/main.c:1565
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:854
-> #2 (&q->elevator_lock){+.+.}-{4:4}:
__mutex_lock_common kernel/locking/mutex.c:646 [inline]
__mutex_lock+0x164/0x1078 kernel/locking/mutex.c:821
mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874
elevator_change+0x188/0x35c block/elevator.c:679
elevator_set_none+0xa8/0x13c block/elevator.c:769
blk_mq_elv_switch_none block/blk-mq.c:5113 [inline]
__blk_mq_update_nr_hw_queues block/blk-mq.c:5158 [inline]
blk_mq_update_nr_hw_queues+0x4c4/0x11e0 block/blk-mq.c:5223
nbd_start_device+0x15c/0xa44 drivers/block/nbd.c:1530
nbd_genl_connect+0xde4/0x12b0 drivers/block/nbd.c:2310
genl_family_rcv_msg_doit+0x1e4/0x2d4 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x43c/0x620 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x238/0x414 net/netlink/af_netlink.c:2575
genl_rcv+0x38/0x50 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1338 [inline]
netlink_unicast+0x600/0x7f8 net/netlink/af_netlink.c:1364
netlink_sendmsg+0x648/0x948 net/netlink/af_netlink.c:1919
sock_sendmsg_nosec net/socket.c:800 [inline]
__sock_sendmsg+0xc8/0x17c net/socket.c:815
__sys_sendto+0x250/0x328 net/socket.c:2281
__do_sys_sendto net/socket.c:2288 [inline]
__se_sys_sendto net/socket.c:2284 [inline]
__arm64_sys_sendto+0xec/0x10c net/socket.c:2284
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
el0_svc+0x60/0x1d8 arch/arm64/kernel/entry-common.c:796
el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:815
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:606
-> #1 (&q->q_usage_counter(io)#33){++++}-{0:0}:
blk_alloc_queue+0x488/0x590 block/blk-core.c:504
blk_mq_alloc_queue+0x148/0x284 block/blk-mq.c:4431
__blk_mq_alloc_disk+0x38/0x10c block/blk-mq.c:4478
nbd_dev_add+0x3d0/0x884 drivers/block/nbd.c:1996
nbd_init+0x174/0x19c drivers/block/nbd.c:2743
do_one_initcall+0x274/0x9f8 init/main.c:1362
do_initcall_level+0x12c/0x1c4 init/main.c:1424
do_initcalls+0x70/0xd0 init/main.c:1440
do_basic_setup+0x7c/0x90 init/main.c:1460
kernel_init_freeable+0x258/0x398 init/main.c:1675
kernel_init+0x28/0x1e0 init/main.c:1565
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:854
-> #0 (fs_reclaim){+.+.}-{0:0}:
check_prev_add kernel/locking/lockdep.c:3209 [inline]
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x1660/0x2b08 kernel/locking/lockdep.c:5288
lock_acquire+0x13c/0x320 kernel/locking/lockdep.c:5942
__fs_reclaim_acquire mm/page_alloc.c:4375 [inline]
fs_reclaim_acquire+0x90/0x110 mm/page_alloc.c:4389
might_alloc include/linux/sched/mm.h:316 [inline]
slab_pre_alloc_hook mm/slub.c:4636 [inline]
slab_alloc_node mm/slub.c:4974 [inline]
kmem_cache_alloc_node_noprof+0x64/0x604 mm/slub.c:5068
kmalloc_reserve+0xc4/0x214 net/core/skbuff.c:615
__alloc_skb+0x230/0x610 net/core/skbuff.c:715
alloc_skb include/linux/skbuff.h:1384 [inline]
alloc_uevent_skb+0x78/0x1ec lib/kobject_uevent.c:289
uevent_net_broadcast_untagged lib/kobject_uevent.c:326 [inline]
kobject_uevent_net_broadcast+0x2d4/0x53c lib/kobject_uevent.c:410
kobject_uevent_env+0x518/0x944 lib/kobject_uevent.c:611
kobject_synth_uevent+0x25c/0x730 lib/kobject_uevent.c:207
uevent_store+0x34/0x84 drivers/base/core.c:2847
dev_attr_store+0x6c/0x90 drivers/base/core.c:2509
sysfs_kf_write+0xe0/0x108 fs/sysfs/file.c:145
kernfs_fop_write_iter+0x260/0x3b8 fs/kernfs/file.c:345
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x51c/0xa0c fs/read_write.c:687
ksys_write+0x12c/0x228 fs/read_write.c:739
__do_sys_write fs/read_write.c:750 [inline]
__se_sys_write fs/read_write.c:747 [inline]
__arm64_sys_write+0x84/0x98 fs/read_write.c:747
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
el0_svc+0x60/0x1d8 arch/arm64/kernel/entry-common.c:796
el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:815
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:606
other info that might help us debug this:
Chain exists of:
fs_reclaim --> cpu_hotplug_lock --> uevent_sock_mutex
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(uevent_sock_mutex);
lock(cpu_hotplug_lock);
lock(uevent_sock_mutex);
lock(fs_reclaim);
*** DEADLOCK ***
locks held by syz-executor796/5066: 5, last CPU#1:
#0: ffff0000d2c57270 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x100/0x144 fs/file.c:1259
#1: ffff0000d0736460 (sb_writers#6){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2756 [inline]
#1: ffff0000d0736460 (sb_writers#6){.+.+}-{0:0}, at: vfs_write+0x248/0xa0c fs/read_write.c:683
#2: ffff0000d1ef6c80 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1b0/0x3b8 fs/kernfs/file.c:336
#3: ffff0000c76cd2d8 (kn->active#4){.+.+}-{0:0}, at: kernfs_get_active_of fs/kernfs/file.c:73 [inline]
#3: ffff0000c76cd2d8 (kn->active#4){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x1f0/0x3b8 fs/kernfs/file.c:337
#4: ffff80008ae5fb20 (uevent_sock_mutex){+.+.}-{4:4}, at: uevent_net_broadcast_untagged lib/kobject_uevent.c:317 [inline]
#4: ffff80008ae5fb20 (uevent_sock_mutex){+.+.}-{4:4}, at: kobject_uevent_net_broadcast+0x24c/0x53c lib/kobject_uevent.c:410
stack backtrace:
CPU: 1 UID: 0 PID: 5066 Comm: syz-executor796 Not tainted syzkaller #0 PREEMPT
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/23/2026
Call trace:
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
__dump_stack+0x30/0x40 lib/dump_stack.c:94
dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
dump_stack+0x1c/0x28 lib/dump_stack.c:129
print_circular_bug+0x328/0x330 kernel/locking/lockdep.c:2087
check_noncircular+0x158/0x174 kernel/locking/lockdep.c:2219
check_prev_add kernel/locking/lockdep.c:3209 [inline]
check_prevs_add kernel/locking/lockdep.c:3328 [inline]
validate_chain kernel/locking/lockdep.c:3952 [inline]
__lock_acquire+0x1660/0x2b08 kernel/locking/lockdep.c:5288
lock_acquire+0x13c/0x320 kernel/locking/lockdep.c:5942
__fs_reclaim_acquire mm/page_alloc.c:4375 [inline]
fs_reclaim_acquire+0x90/0x110 mm/page_alloc.c:4389
might_alloc include/linux/sched/mm.h:316 [inline]
slab_pre_alloc_hook mm/slub.c:4636 [inline]
slab_alloc_node mm/slub.c:4974 [inline]
kmem_cache_alloc_node_noprof+0x64/0x604 mm/slub.c:5068
kmalloc_reserve+0xc4/0x214 net/core/skbuff.c:615
__alloc_skb+0x230/0x610 net/core/skbuff.c:715
alloc_skb include/linux/skbuff.h:1384 [inline]
alloc_uevent_skb+0x78/0x1ec lib/kobject_uevent.c:289
uevent_net_broadcast_untagged lib/kobject_uevent.c:326 [inline]
kobject_uevent_net_broadcast+0x2d4/0x53c lib/kobject_uevent.c:410
kobject_uevent_env+0x518/0x944 lib/kobject_uevent.c:611
kobject_synth_uevent+0x25c/0x730 lib/kobject_uevent.c:207
uevent_store+0x34/0x84 drivers/base/core.c:2847
dev_attr_store+0x6c/0x90 drivers/base/core.c:2509
sysfs_kf_write+0xe0/0x108 fs/sysfs/file.c:145
kernfs_fop_write_iter+0x260/0x3b8 fs/kernfs/file.c:345
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x51c/0xa0c fs/read_write.c:687
ksys_write+0x12c/0x228 fs/read_write.c:739
__do_sys_write fs/read_write.c:750 [inline]
__se_sys_write fs/read_write.c:747 [inline]
__arm64_sys_write+0x84/0x98 fs/read_write.c:747
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
el0_svc+0x60/0x1d8 arch/arm64/kernel/entry-common.c:796
el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:815
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:606
---
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2026-10-27 14:19 [syzbot] [driver-core?] possible deadlock in device_register (2) syzbot
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