=============================
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 syz.0.1814/12184:
 #0: ffffffff8c31eb20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
 #1: ffff88807cc15948 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: net_tx_action+0x6d9/0x880 net/core/dev.c:5154
 #2: ffff88807cc15908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 #2: ffff88807cc15908 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x311/0x4b0 net/sched/sch_generic.c:357
 #3: ffffffff8c31eb20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312

stack backtrace:
CPU: 1 PID: 12184 Comm: syz.0.1814 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
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
 cake_dequeue+0x1bd6/0x4b10 net/sched/sch_cake.c:2205
 qdisc_peek_dequeued+0x6e/0x1f0 include/net/sch_generic.h:1125
 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:__syscall_enter_from_user_work kernel/entry/common.c:93 [inline]
RIP: 0010:syscall_enter_from_user_mode+0x2a/0x70 kernel/entry/common.c:114
Code: 41 56 53 48 89 f3 49 89 fe 48 8b 7c 24 10 e8 3d f6 ff ff eb 31 eb 35 e8 74 7d c2 f7 e8 6f 7b c2 f7 fb 65 48 8b 05 d6 8a 45 76 <48> 8b 70 08 40 f6 c6 3f 74 0b 4c 89 f7 5b 41 5e e9 11 7b aa f7 48
RSP: 0018:ffffc90003de7f08 EFLAGS: 00000286
RAX: ffff888047b3bb80 RBX: 00000000000000ca RCX: b1e2bdad9383d600
RDX: dffffc0000000000 RSI: ffffffff8a2b2800 RDI: ffffffff8a79fe40
RBP: ffffc90003de7f48 R08: ffffffff8d89f06f R09: 1ffffffff1b13e0d
R10: dffffc0000000000 R11: fffffbfff1b13e0e R12: 0000000000000000
R13: 0000000000000000 R14: ffffc90003de7f58 R15: 0000000000000000
 do_syscall_64+0x24/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f9686794dd9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc60760f98 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: ffffffffffffffda RBX: 00000000000938e8 RCX: 00007f9686794dd9
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f9686a0dfac
RBP: 0000000000000fd2 R08: 00172fc7bbef1cbe R09: 0000000000000000
R10: 00007ffc607610a0 R11: 0000000000000246 R12: 00007ffc607610c0
R13: 00007f9686a0dfac R14: 00000000000948ba R15: 00007ffc607610a0
 </TASK>
----------------
Code disassembly (best guess):
   0:	41 56                	push   %r14
   2:	53                   	push   %rbx
   3:	48 89 f3             	mov    %rsi,%rbx
   6:	49 89 fe             	mov    %rdi,%r14
   9:	48 8b 7c 24 10       	mov    0x10(%rsp),%rdi
   e:	e8 3d f6 ff ff       	call   0xfffff650
  13:	eb 31                	jmp    0x46
  15:	eb 35                	jmp    0x4c
  17:	e8 74 7d c2 f7       	call   0xf7c27d90
  1c:	e8 6f 7b c2 f7       	call   0xf7c27b90
  21:	fb                   	sti
  22:	65 48 8b 05 d6 8a 45 	mov    %gs:0x76458ad6(%rip),%rax        # 0x76458b00
  29:	76
* 2a:	48 8b 70 08          	mov    0x8(%rax),%rsi <-- trapping instruction
  2e:	40 f6 c6 3f          	test   $0x3f,%sil
  32:	74 0b                	je     0x3f
  34:	4c 89 f7             	mov    %r14,%rdi
  37:	5b                   	pop    %rbx
  38:	41 5e                	pop    %r14
  3a:	e9 11 7b aa f7       	jmp    0xf7aa7b50
  3f:	48                   	rex.W