possible deadlock in __alloc_workqueue (3)

Status: upstream: reported on 2026/07/20 22:51
Subsystems: crypto
Labels: prio:normal
[Documentation on labels]
Reported-by: syzbot+5f117b3024eab6a14c35@syzkaller.appspotmail.com
First crash: 51d, last: 5h43m
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ID Workflow Result Correct Bug Created Started Finished Revision
23eece1b assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ possible deadlock in __alloc_workqueue (3) 2026/07/18 00:01 2026/07/18 00:01 2026/07/18 00:08 8aaff637
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Title Replies (including bot) Last reply
[syzbot] [crypto?] possible deadlock in __alloc_workqueue (3) 0 (1) 2026/07/20 22:51
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in __alloc_workqueue kernel 4 6 335d 357d 29/29 fixed on 2025/10/29 21:02

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
kworker/0:5/5698 is trying to acquire lock:
ffffffff8efc9ea0 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:316 [inline]
ffffffff8efc9ea0 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4636 [inline]
ffffffff8efc9ea0 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:4974 [inline]
ffffffff8efc9ea0 (fs_reclaim){+.+.}-{0:0}, at: __do_kmalloc_node mm/slub.c:5413 [inline]
ffffffff8efc9ea0 (fs_reclaim){+.+.}-{0:0}, at: __kmalloc_noprof+0xce/0x840 mm/slub.c:5439

but task is already holding lock:
ffffffff8ec92f60 (wq_pool_mutex){+.+.}-{4:4}, at: __alloc_workqueue+0x839/0x1950 kernel/workqueue.c:5982

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #8 (wq_pool_mutex){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5908 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       __alloc_workqueue+0x839/0x1950 kernel/workqueue.c:5982
       alloc_workqueue_va kernel/workqueue.c:6033 [inline]
       alloc_workqueue_noprof+0xc7/0x130 kernel/workqueue.c:6049
       padata_alloc+0xc7/0x400 kernel/padata.c:964
       pcrypt_init_padata+0x19/0xf5 crypto/pcrypt.c:335
       pcrypt_init+0x72/0xf0 crypto/pcrypt.c:360
       do_one_initcall+0x11c/0x6f0 init/main.c:1357
       do_initcall_level init/main.c:1419 [inline]
       do_initcalls init/main.c:1435 [inline]
       do_basic_setup init/main.c:1455 [inline]
       kernel_init_freeable+0x6ea/0x7b0 init/main.c:1670
       kernel_init+0x21/0x1e0 init/main.c:1560
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #7 (cpu_hotplug_lock){++++}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5908 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
       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_disable+0x12/0x20 kernel/jump_label.c:247
       __inet_hash_connect+0x143e/0x2000 net/ipv4/inet_hashtables.c:1081
       tcp_v4_connect+0xeb3/0x1b40 net/ipv4/tcp_ipv4.c:306
       __inet_stream_connect+0x208/0xf90 net/ipv4/af_inet.c:684
       inet_stream_connect+0x57/0xa0 net/ipv4/af_inet.c:755
       connect_socket net/socket.c:2141 [inline]
       connect_socket net/socket.c:2131 [inline]
       __sys_connect_file+0x146/0x1a0 net/socket.c:2166
       __sys_connect+0x141/0x170 net/socket.c:2183
       __do_sys_connect net/socket.c:2189 [inline]
       __se_sys_connect net/socket.c:2186 [inline]
       __x64_sys_connect+0x72/0xb0 net/socket.c:2186
       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 (sk_lock-AF_INET){+.+.}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5908 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
       lock_sock_nested+0x41/0xf0 net/core/sock.c:3827
       lock_sock include/net/sock.h:1713 [inline]
       inet_shutdown+0x67/0x410 net/ipv4/af_inet.c:913
       nbd_mark_nsock_dead+0xae/0x5c0 drivers/block/nbd.c:319
       recv_work+0x5fb/0x8c0 drivers/block/nbd.c:1030
       process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       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 (&nsock->tx_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5908 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 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:3396
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       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 (&cmd->lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5908 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 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:3396
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       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

-> #3 (set->srcu){.+.+}-{0:0}:
       lock_sync kernel/locking/lockdep.c:5957 [inline]
       lock_sync+0xb5/0x120 kernel/locking/lockdep.c:5945
       srcu_lock_sync include/linux/srcu.h:210 [inline]
       __synchronize_srcu+0xa2/0x300 kernel/rcu/srcutree.c:1462
       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:1357
       do_initcall_level init/main.c:1419 [inline]
       do_initcalls init/main.c:1435 [inline]
       do_basic_setup init/main.c:1455 [inline]
       kernel_init_freeable+0x6ea/0x7b0 init/main.c:1670
       kernel_init+0x21/0x1e0 init/main.c:1560
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #2 (&q->elevator_lock){+.+.}-{4:4}:
       lock_acquire kernel/locking/lockdep.c:5908 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       elevator_change+0x1bc/0x530 block/elevator.c:679
       elv_iosched_store+0x3be/0x460 block/elevator.c:826
       queue_attr_store+0x25f/0x2f0 block/blk-sysfs.c:906
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
       kernfs_fop_write_iter+0x3e0/0x5f0 fs/kernfs/file.c:345
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x6af/0x1050 fs/read_write.c:687
       ksys_write+0x12a/0x250 fs/read_write.c:739
       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

-> #1 (&q->q_usage_counter(io)#66){++++}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5908 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
       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
       null_add_dev+0xdf8/0x1df0 drivers/block/null_blk/main.c:2017
       null_create_dev drivers/block/null_blk/main.c:2114 [inline]
       null_init+0x36b/0x460 drivers/block/null_blk/main.c:2178
       do_one_initcall+0x11c/0x6f0 init/main.c:1357
       do_initcall_level init/main.c:1419 [inline]
       do_initcalls init/main.c:1435 [inline]
       do_basic_setup init/main.c:1455 [inline]
       kernel_init_freeable+0x6ea/0x7b0 init/main.c:1670
       kernel_init+0x21/0x1e0 init/main.c:1560
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (fs_reclaim){+.+.}-{0:0}:
       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:5254
       lock_acquire kernel/locking/lockdep.c:5908 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
       __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:316 [inline]
       slab_pre_alloc_hook mm/slub.c:4636 [inline]
       slab_alloc_node mm/slub.c:4974 [inline]
       __do_kmalloc_node mm/slub.c:5413 [inline]
       __kmalloc_noprof+0xce/0x840 mm/slub.c:5439
       _kmalloc_noprof include/linux/slab.h:995 [inline]
       _kzalloc_noprof include/linux/slab.h:1312 [inline]
       apply_wqattrs_prepare+0xfe/0xbb0 kernel/workqueue.c:5498
       apply_workqueue_attrs_locked+0x64/0xe0 kernel/workqueue.c:5584
       alloc_and_link_pwqs kernel/workqueue.c:5731 [inline]
       __alloc_workqueue+0x9a7/0x1950 kernel/workqueue.c:5984
       alloc_workqueue_va kernel/workqueue.c:6033 [inline]
       alloc_workqueue_noprof+0xc7/0x130 kernel/workqueue.c:6049
       hci_register_dev+0x1cd/0xc90 net/bluetooth/hci_core.c:2568
       __vhci_create_device+0x357/0x880 drivers/bluetooth/hci_vhci.c:461
       vhci_create_device drivers/bluetooth/hci_vhci.c:489 [inline]
       vhci_open_timeout+0x30/0x40 drivers/bluetooth/hci_vhci.c:646
       process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       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:
  fs_reclaim --> cpu_hotplug_lock --> wq_pool_mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(wq_pool_mutex);
                               lock(cpu_hotplug_lock);
                               lock(wq_pool_mutex);
  lock(fs_reclaim);

 *** DEADLOCK ***

locks held by kworker/0:5/5698: 4, last CPU#0:
 #0: ffff88801c057140 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x1466/0x1b10 kernel/workqueue.c:3371
 #1: ffffc900042a7d08 ((work_completion)(&(&data->open_timeout)->work)){+.+.}-{0:0}, at: process_one_work+0xa2c/0x1b10 kernel/workqueue.c:3372
 #2: ffff88804cb89910 (&data->open_mutex){+.+.}-{4:4}, at: vhci_create_device drivers/bluetooth/hci_vhci.c:488 [inline]
 #2: ffff88804cb89910 (&data->open_mutex){+.+.}-{4:4}, at: vhci_open_timeout+0x26/0x40 drivers/bluetooth/hci_vhci.c:646
 #3: ffffffff8ec92f60 (wq_pool_mutex){+.+.}-{4:4}, at: __alloc_workqueue+0x839/0x1950 kernel/workqueue.c:5982

stack backtrace:
CPU: 0 UID: 0 PID: 5698 Comm: kworker/0:5 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/05/2026
Workqueue: events vhci_open_timeout
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:5254
 lock_acquire kernel/locking/lockdep.c:5908 [inline]
 lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
 __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:316 [inline]
 slab_pre_alloc_hook mm/slub.c:4636 [inline]
 slab_alloc_node mm/slub.c:4974 [inline]
 __do_kmalloc_node mm/slub.c:5413 [inline]
 __kmalloc_noprof+0xce/0x840 mm/slub.c:5439
 _kmalloc_noprof include/linux/slab.h:995 [inline]
 _kzalloc_noprof include/linux/slab.h:1312 [inline]
 apply_wqattrs_prepare+0xfe/0xbb0 kernel/workqueue.c:5498
 apply_workqueue_attrs_locked+0x64/0xe0 kernel/workqueue.c:5584
 alloc_and_link_pwqs kernel/workqueue.c:5731 [inline]
 __alloc_workqueue+0x9a7/0x1950 kernel/workqueue.c:5984
 alloc_workqueue_va kernel/workqueue.c:6033 [inline]
 alloc_workqueue_noprof+0xc7/0x130 kernel/workqueue.c:6049
 hci_register_dev+0x1cd/0xc90 net/bluetooth/hci_core.c:2568
 __vhci_create_device+0x357/0x880 drivers/bluetooth/hci_vhci.c:461
 vhci_create_device drivers/bluetooth/hci_vhci.c:489 [inline]
 vhci_open_timeout+0x30/0x40 drivers/bluetooth/hci_vhci.c:646
 process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
 process_scheduled_works kernel/workqueue.c:3479 [inline]
 worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
 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>

Crashes (15):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/02 09:27 upstream 89a312991dc6 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root possible deadlock in __alloc_workqueue
2026/09/05 11:27 net 80dd7e754b3a 4f7b22a0 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce possible deadlock in __alloc_workqueue
2026/09/01 20:17 net 1d2929d0850f 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce possible deadlock in __alloc_workqueue
2026/08/30 13:22 net 2188569e7e1b 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce possible deadlock in __alloc_workqueue
2026/08/04 17:44 net cf6f8b29befb d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce possible deadlock in __alloc_workqueue
2026/09/06 08:29 net-next d76beefca7e5 4f7b22a0 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce possible deadlock in __alloc_workqueue
2026/09/05 18:03 net-next 9eab111e7657 4f7b22a0 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce possible deadlock in __alloc_workqueue
2026/09/05 09:50 net-next 9eab111e7657 4f7b22a0 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce possible deadlock in __alloc_workqueue
2026/09/03 11:58 net-next d0ec95a8a4e7 6a988719 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce possible deadlock in __alloc_workqueue
2026/09/02 17:23 net-next c29b37ed7a4d 85995287 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce possible deadlock in __alloc_workqueue
2026/09/01 06:47 net-next 25c1f6111034 316d9396 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce possible deadlock in __alloc_workqueue
2026/08/28 02:03 net-next 1b78070aaef6 e2fa417d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce possible deadlock in __alloc_workqueue
2026/08/27 00:44 net-next 91ec20351349 a2b77b9e .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce possible deadlock in __alloc_workqueue
2026/07/16 22:49 net-next f6f3b36c15ed 8f30cfd7 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce possible deadlock in __alloc_workqueue
2026/09/04 15:32 linux-next 9d80aa4617b3 3f042c7b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root possible deadlock in __alloc_workqueue
* Struck through repros no longer work on HEAD.