=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
net/sched/sch_api.c:304 suspicious rcu_dereference_protected() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
7 locks held by kworker/0:0/7:
 #0: ffff888016870938 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x760/0x1000 kernel/workqueue.c:-1
 #1: ffffc90000cc7d00 ((work_completion)(&w->work)#2){+.+.}-{0:0}, at: process_one_work+0x7a3/0x1000 kernel/workqueue.c:2285
 #2: ffffffff8d29dde8 (nf_conntrack_mutex){+.+.}-{3:3}, at: nf_ct_iterate_cleanup+0x47/0x3c0 net/netfilter/nf_conntrack_core.c:2380
 #3: ffffffff8c11c760 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
 #4: ffff8880245a4948 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: net_tx_action+0x6bc/0x870 net/core/dev.c:5128
 #5: ffff8880245a4908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 #5: ffff8880245a4908 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x305/0x4a0 net/sched/sch_generic.c:354
 #6: ffffffff8c11c760 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312

stack backtrace:
CPU: 0 PID: 7 Comm: kworker/0:0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: events iterate_cleanup_work
Call Trace:
 <IRQ>
 dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
 qdisc_lookup+0xa6/0x650 net/sched/sch_api.c:304
 qdisc_tree_reduce_backlog+0x190/0x430 net/sched/sch_api.c:793
 cake_dequeue+0x1b8f/0x4aa0 net/sched/sch_cake.c:2199
 qdisc_peek_dequeued+0x6e/0x1f0 include/net/sch_generic.h:1115
 tbf_dequeue+0x7d/0xce0 net/sched/sch_tbf.c:265
 dequeue_skb net/sched/sch_generic.c:292 [inline]
 qdisc_restart net/sched/sch_generic.c:397 [inline]
 __qdisc_run+0x237/0x1480 net/sched/sch_generic.c:415
 qdisc_run+0x103/0x2f0 include/net/pkt_sched.h:132
 net_tx_action+0x6bc/0x870 net/core/dev.c:5128
 handle_softirqs+0x328/0x820 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x12f/0x220 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:get_next_corpse net/netfilter/nf_conntrack_core.c:-1 [inline]
RIP: 0010:nf_ct_iterate_cleanup+0x6a/0x3c0 net/netfilter/nf_conntrack_core.c:2381
Code: 31 f6 e8 79 f1 9a 01 8b 1d 47 48 53 05 31 ff 89 de e8 2a df 60 f9 85 db 0f 84 27 03 00 00 49 bc 00 00 00 00 00 fc ff df 31 db <89> d8 89 d9 25 ff 03 00 00 c1 e0 06 48 8d 80 80 4a e6 8b 48 89 44
RSP: 0018:ffffc90000cc7ac8 EFLAGS: 00000293
RAX: ffffffff8816f362 RBX: 000000000001ad49 RCX: ffff8880175c3b80
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: 1ffff1100565ad48 R08: dffffc0000000000 R09: fffffbfff1ff7c2b
R10: fffffbfff1ff7c2b R11: 1ffffffff1ff7c2a R12: dffffc0000000000
R13: 0000000000000001 R14: ffffc90000cc7b60 R15: ffffffff8816f3b0
 nf_ct_iterate_cleanup_net+0x10f/0x180 net/netfilter/nf_conntrack_core.c:2465
 iterate_cleanup_work+0x66/0x120 net/netfilter/nf_nat_masquerade.c:83
 process_one_work+0x863/0x1000 kernel/workqueue.c:2310
 worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
----------------
Code disassembly (best guess):
   0:	31 f6                	xor    %esi,%esi
   2:	e8 79 f1 9a 01       	call   0x19af180
   7:	8b 1d 47 48 53 05    	mov    0x5534847(%rip),%ebx        # 0x5534854
   d:	31 ff                	xor    %edi,%edi
   f:	89 de                	mov    %ebx,%esi
  11:	e8 2a df 60 f9       	call   0xf960df40
  16:	85 db                	test   %ebx,%ebx
  18:	0f 84 27 03 00 00    	je     0x345
  1e:	49 bc 00 00 00 00 00 	movabs $0xdffffc0000000000,%r12
  25:	fc ff df
  28:	31 db                	xor    %ebx,%ebx
* 2a:	89 d8                	mov    %ebx,%eax <-- trapping instruction
  2c:	89 d9                	mov    %ebx,%ecx
  2e:	25 ff 03 00 00       	and    $0x3ff,%eax
  33:	c1 e0 06             	shl    $0x6,%eax
  36:	48 8d 80 80 4a e6 8b 	lea    -0x7419b580(%rax),%rax
  3d:	48                   	rex.W
  3e:	89                   	.byte 0x89
  3f:	44                   	rex.R