rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	1-...!: (0 ticks this GP) idle=7f6/1/0x4000000000000000 softirq=26470/26470 fqs=0 
	(detected by 0, t=10502 jiffies, g=41641, q=75)

============================================
WARNING: possible recursive locking detected
5.10.0-rc7-next-20201208-syzkaller #0 Not tainted
--------------------------------------------
kworker/0:7/10470 is trying to acquire lock:
ffffffff8b797b58 (rcu_node_0){-.-.}-{2:2}, at: rcu_dump_cpu_stacks+0xaf/0x2a7 kernel/rcu/tree_stall.h:337

but task is already holding lock:
ffffffff8b797b58 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:546 [inline]
ffffffff8b797b58 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:711 [inline]
ffffffff8b797b58 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3792 [inline]
ffffffff8b797b58 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq.cold+0x133/0x12ae kernel/rcu/tree.c:2593

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

       CPU0
       ----
  lock(rcu_node_0);
  lock(rcu_node_0);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

6 locks held by kworker/0:7/10470:
 #0: ffff888010862d38 ((wq_completion)events){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff888010862d38 ((wq_completion)events){+.+.}-{0:0}, at: atomic64_set include/asm-generic/atomic-instrumented.h:856 [inline]
 #0: ffff888010862d38 ((wq_completion)events){+.+.}-{0:0}, at: atomic_long_set include/asm-generic/atomic-long.h:41 [inline]
 #0: ffff888010862d38 ((wq_completion)events){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:616 [inline]
 #0: ffff888010862d38 ((wq_completion)events){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #0: ffff888010862d38 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x871/0x1630 kernel/workqueue.c:2246
 #1: ffffc90002b17da8 ((kfence_timer).work){+.+.}-{0:0}, at: process_one_work+0x8a5/0x1630 kernel/workqueue.c:2250
 #2: ffffffff8b62a230 (cpu_hotplug_lock){++++}-{0:0}, at: static_key_enable+0xe/0x20 kernel/jump_label.c:189
 #3: ffffffff8b874e28 (jump_label_mutex){+.+.}-{3:3}, at: jump_label_lock kernel/jump_label.c:27 [inline]
 #3: ffffffff8b874e28 (jump_label_mutex){+.+.}-{3:3}, at: static_key_enable_cpuslocked+0xcf/0x280 kernel/jump_label.c:174
 #4: ffffffff8b64d888 (text_mutex){+.+.}-{3:3}, at: arch_jump_label_transform_apply+0xe/0x20 arch/x86/kernel/jump_label.c:125
 #5: ffffffff8b797b58 (rcu_node_0){-.-.}-{2:2}, at: print_other_cpu_stall kernel/rcu/tree_stall.h:546 [inline]
 #5: ffffffff8b797b58 (rcu_node_0){-.-.}-{2:2}, at: check_cpu_stall kernel/rcu/tree_stall.h:711 [inline]
 #5: ffffffff8b797b58 (rcu_node_0){-.-.}-{2:2}, at: rcu_pending kernel/rcu/tree.c:3792 [inline]
 #5: ffffffff8b797b58 (rcu_node_0){-.-.}-{2:2}, at: rcu_sched_clock_irq.cold+0x133/0x12ae kernel/rcu/tree.c:2593

stack backtrace:
CPU: 0 PID: 10470 Comm: kworker/0:7 Not tainted 5.10.0-rc7-next-20201208-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events toggle_allocation_gate
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:120
 print_deadlock_bug kernel/locking/lockdep.c:2761 [inline]
 check_deadlock kernel/locking/lockdep.c:2804 [inline]
 validate_chain kernel/locking/lockdep.c:3595 [inline]
 __lock_acquire.cold+0x115/0x3e6 kernel/locking/lockdep.c:4832
 lock_acquire kernel/locking/lockdep.c:5437 [inline]
 lock_acquire+0x29d/0x750 kernel/locking/lockdep.c:5402
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x39/0x50 kernel/locking/spinlock.c:159
 rcu_dump_cpu_stacks+0xaf/0x2a7 kernel/rcu/tree_stall.h:337
 print_other_cpu_stall kernel/rcu/tree_stall.h:564 [inline]
 check_cpu_stall kernel/rcu/tree_stall.h:711 [inline]
 rcu_pending kernel/rcu/tree.c:3792 [inline]
 rcu_sched_clock_irq.cold+0x86e/0x12ae kernel/rcu/tree.c:2593
 update_process_times+0x16d/0x200 kernel/time/timer.c:1782
 tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:206
 tick_sched_timer+0x1b0/0x2d0 kernel/time/tick-sched.c:1356
 __run_hrtimer kernel/time/hrtimer.c:1519 [inline]
 __hrtimer_run_queues+0x1c0/0xea0 kernel/time/hrtimer.c:1583
 hrtimer_interrupt+0x334/0x960 kernel/time/hrtimer.c:1645
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1085 [inline]
 __sysvec_apic_timer_interrupt+0x146/0x550 arch/x86/kernel/apic/apic.c:1102
 asm_call_irq_on_stack+0xf/0x20
 </IRQ>
 __run_sysvec_on_irqstack arch/x86/include/asm/irq_stack.h:37 [inline]
 run_sysvec_on_irqstack_cond arch/x86/include/asm/irq_stack.h:89 [inline]
 sysvec_apic_timer_interrupt+0xbd/0x100 arch/x86/kernel/apic/apic.c:1096
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:628
RIP: 0010:csd_lock_wait kernel/smp.c:227 [inline]
RIP: 0010:smp_call_function_single+0x1b0/0x4b0 kernel/smp.c:512
Code: 10 8b 7c 24 1c 48 8d 74 24 40 48 89 44 24 50 48 8b 44 24 08 48 89 44 24 58 e8 0c fb ff ff 41 89 c5 eb 07 e8 82 80 0b 00 f3 90 <44> 8b 64 24 48 31 ff 41 83 e4 01 44 89 e6 e8 7d 8c 0b 00 45 85 e4
RSP: 0018:ffffc90002b17940 EFLAGS: 00000293
RAX: 0000000000000000 RBX: 1ffff92000562f2c RCX: 0000000000000000
RDX: ffff888020a58000 RSI: ffffffff8166c67e RDI: 0000000000000003
RBP: ffffc90002b17a08 R08: 0000000000000000 R09: ffffffff8f4fe767
R10: ffffffff8166c693 R11: 0000000000000000 R12: 0000000000000001
R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000008
 smp_call_function_many_cond+0x27d/0x9e0 kernel/smp.c:648
 smp_call_function_many kernel/smp.c:711 [inline]
 smp_call_function kernel/smp.c:733 [inline]
 on_each_cpu+0x4f/0x110 kernel/smp.c:832
 text_poke_sync arch/x86/kernel/alternative.c:1008 [inline]
 text_poke_bp_batch+0x1a7/0x550 arch/x86/kernel/alternative.c:1193
 text_poke_flush arch/x86/kernel/alternative.c:1347 [inline]
 text_poke_flush arch/x86/kernel/alternative.c:1344 [inline]
 text_poke_finish+0x16/0x30 arch/x86/kernel/alternative.c:1354
 arch_jump_label_transform_apply+0x13/0x20 arch/x86/kernel/jump_label.c:126
 jump_label_update kernel/jump_label.c:814 [inline]
 jump_label_update+0x1b3/0x3a0 kernel/jump_label.c:793
 static_key_enable_cpuslocked+0x1cf/0x280 kernel/jump_label.c:177
 static_key_enable+0x16/0x20 kernel/jump_label.c:190
 toggle_allocation_gate mm/kfence/core.c:594 [inline]
 toggle_allocation_gate+0x116/0x260 mm/kfence/core.c:587
 process_one_work+0x98d/0x1630 kernel/workqueue.c:2275
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
 kthread+0x3b1/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296