=============================
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
4 locks held by rcu_preempt/15:
 #0: ffffffff8c31eaa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
 #1: ffff888049713148 (dev->qdisc_running_key ?: &qdisc_running_key){+..-}-{0:0}, at: net_tx_action+0x6d9/0x880 net/core/dev.c:5154
 #2: ffff888049713108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 #2: ffff888049713108 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x311/0x4b0 net/sched/sch_generic.c:357
 #3: ffffffff8c31eaa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312

stack backtrace:
CPU: 0 PID: 15 Comm: rcu_preempt Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <IRQ>
 dump_stack_lvl+0x188/0x250 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:783
 fq_codel_dequeue+0x26c5/0x28d0 net/sched/sch_fq_codel.c:319
 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:295 [inline]
 qdisc_restart net/sched/sch_generic.c:400 [inline]
 __qdisc_run+0x236/0x1490 net/sched/sch_generic.c:418
 qdisc_run+0x103/0x2f0 include/net/pkt_sched.h:131
 net_tx_action+0x6d9/0x880 net/core/dev.c:5154
 handle_softirqs+0x339/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 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:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:169 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x25/0x40 kernel/locking/spinlock.c:202
Code: 00 00 00 66 90 53 48 89 fb 48 83 c7 18 48 8b 74 24 08 e8 be a9 97 f7 48 89 df e8 f6 81 98 f7 e8 61 74 b9 f7 fb bf 01 00 00 00 <e8> a6 89 8c f7 65 8b 05 47 97 3c 76 85 c0 74 02 5b c3 e8 94 a4 3a
RSP: 0018:ffffc90000d47d50 EFLAGS: 00000282
RAX: 35d3e7552c9db500 RBX: ffffffff8c322f00 RCX: 35d3e7552c9db500
RDX: dffffc0000000000 RSI: ffffffff8a2b2780 RDI: 0000000000000001
RBP: ffffffff8c322f00 R08: ffffffff8c322f03 R09: 1ffffffff18645e0
R10: dffffc0000000000 R11: fffffbfff18645e1 R12: ffffffff8c322fb4
R13: 1ffffffff18645e9 R14: dffffc0000000000 R15: ffffffff8c322f98
 rcu_gp_cleanup+0x404/0xa90 kernel/rcu/tree.c:2076
 rcu_gp_kthread+0xa9/0x370 kernel/rcu/tree.c:2149
 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:	00 00                	add    %al,(%rax)
   2:	00 66 90             	add    %ah,-0x70(%rsi)
   5:	53                   	push   %rbx
   6:	48 89 fb             	mov    %rdi,%rbx
   9:	48 83 c7 18          	add    $0x18,%rdi
   d:	48 8b 74 24 08       	mov    0x8(%rsp),%rsi
  12:	e8 be a9 97 f7       	call   0xf797a9d5
  17:	48 89 df             	mov    %rbx,%rdi
  1a:	e8 f6 81 98 f7       	call   0xf7988215
  1f:	e8 61 74 b9 f7       	call   0xf7b97485
  24:	fb                   	sti
  25:	bf 01 00 00 00       	mov    $0x1,%edi
* 2a:	e8 a6 89 8c f7       	call   0xf78c89d5 <-- trapping instruction
  2f:	65 8b 05 47 97 3c 76 	mov    %gs:0x763c9747(%rip),%eax        # 0x763c977d
  36:	85 c0                	test   %eax,%eax
  38:	74 02                	je     0x3c
  3a:	5b                   	pop    %rbx
  3b:	c3                   	ret
  3c:	e8                   	.byte 0xe8
  3d:	94                   	xchg   %eax,%esp
  3e:	a4                   	movsb  %ds:(%rsi),%es:(%rdi)
  3f:	3a                   	.byte 0x3a