============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
ktimers/0/16 is trying to acquire lock:
ffff8880b873a990 (&pool->cb_lock){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:45 [inline]
ffff8880b873a990 (&pool->cb_lock){+...}-{3:3}, at: worker_lock_callback kernel/workqueue.c:3144 [inline]
ffff8880b873a990 (&pool->cb_lock){+...}-{3:3}, at: bh_worker+0x7d/0x880 kernel/workqueue.c:3688

but task is already holding lock:
ffff8880b863a990 (&pool->cb_lock){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:45 [inline]
ffff8880b863a990 (&pool->cb_lock){+...}-{3:3}, at: worker_lock_callback kernel/workqueue.c:3144 [inline]
ffff8880b863a990 (&pool->cb_lock){+...}-{3:3}, at: bh_worker+0x7d/0x880 kernel/workqueue.c:3688

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&pool->cb_lock);
  lock(&pool->cb_lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

6 locks held by ktimers/0/16:
 #0: ffffffff8e059220 (local_bh){.+.+}-{1:3}, at: __local_bh_disable_ip+0x3c/0x420 kernel/softirq.c:163
 #1: ffffffff8e1c3000 (rcu_read_lock){....}-{1:3}, at: __local_bh_disable_ip+0x3c/0x420 kernel/softirq.c:163
 #2: ffff8880b863a990 (&pool->cb_lock){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:45 [inline]
 #2: ffff8880b863a990 (&pool->cb_lock){+...}-{3:3}, at: worker_lock_callback kernel/workqueue.c:3144 [inline]
 #2: ffff8880b863a990 (&pool->cb_lock){+...}-{3:3}, at: bh_worker+0x7d/0x880 kernel/workqueue.c:3688
 #3: ffffffff8e1c3000 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #3: ffffffff8e1c3000 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
 #3: ffffffff8e1c3000 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline]
 #3: ffffffff8e1c3000 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1e0/0x400 kernel/locking/spinlock_rt.c:57
 #4: ffff88813ff19d38 ((wq_completion)events_bh){+...}-{0:0}, at: process_one_work kernel/workqueue.c:3297 [inline]
 #4: ffff88813ff19d38 ((wq_completion)events_bh){+...}-{0:0}, at: process_scheduled_works+0xa20/0x14e0 kernel/workqueue.c:3405
 #5: ffffc90000157ba0 ((work_completion)(&dead_work.work)){+...}-{0:0}, at: process_one_work kernel/workqueue.c:3297 [inline]
 #5: ffffc90000157ba0 ((work_completion)(&dead_work.work)){+...}-{0:0}, at: process_scheduled_works+0xa20/0x14e0 kernel/workqueue.c:3405

stack backtrace:
CPU: 0 UID: 0 PID: 16 Comm: ktimers/0 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_deadlock_bug+0x279/0x290 kernel/locking/lockdep.c:3041
 check_deadlock kernel/locking/lockdep.c:3093 [inline]
 validate_chain kernel/locking/lockdep.c:3895 [inline]
 __lock_acquire+0x24df/0x2ce0 kernel/locking/lockdep.c:5237
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
 rt_spin_lock+0x83/0x400 kernel/locking/spinlock_rt.c:56
 spin_lock include/linux/spinlock_rt.h:45 [inline]
 worker_lock_callback kernel/workqueue.c:3144 [inline]
 bh_worker+0x7d/0x880 kernel/workqueue.c:3688
 drain_dead_softirq_workfn+0x95/0x220 kernel/workqueue.c:3763
 process_one_work kernel/workqueue.c:3322 [inline]
 process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
 bh_worker+0x46a/0x880 kernel/workqueue.c:3708
 tasklet_action+0xc/0x70 kernel/softirq.c:965
 handle_softirqs+0x1d9/0x6c0 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 run_ktimerd+0x69/0x100 kernel/softirq.c:1151
 smpboot_thread_fn+0x57c/0xa80 kernel/smpboot.c:160
 kthread+0x388/0x470 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>
BUG: workqueue leaked atomic, lock or RCU: ktimers/0[16]
     preempt=0x00000000 lock=4->0 RCU=2->2 workfn=drain_dead_softirq_workfn
INFO: lockdep is turned off.
CPU: 0 UID: 0 PID: 16 Comm: ktimers/0 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 process_one_work kernel/workqueue.c:3343 [inline]
 process_scheduled_works+0x1161/0x14e0 kernel/workqueue.c:3405
 bh_worker+0x46a/0x880 kernel/workqueue.c:3708
 tasklet_action+0xc/0x70 kernel/softirq.c:965
 handle_softirqs+0x1d9/0x6c0 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 run_ktimerd+0x69/0x100 kernel/softirq.c:1151
 smpboot_thread_fn+0x57c/0xa80 kernel/smpboot.c:160
 kthread+0x388/0x470 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>
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