=============================
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 udevd/3560:
 #0: ffffffff8c31f320 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
 #1: ffff88801fff7148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: net_tx_action+0x6d9/0x880 net/core/dev.c:5154
 #2: ffff88801fff7108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 #2: ffff88801fff7108 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x311/0x4b0 net/sched/sch_generic.c:357
 #3: ffffffff8c31f320 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312

stack backtrace:
CPU: 0 PID: 3560 Comm: udevd 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:preempt_schedule_irq+0xb6/0x160 kernel/sched/core.c:6799
Code: 00 00 43 c6 44 37 04 f8 74 0b 0f 0b 48 f7 03 08 00 00 00 74 7f bf 01 00 00 00 e8 15 4f 8d f7 e8 e0 3e ba f7 fb bf 01 00 00 00 <e8> 65 b5 ff ff 43 c6 44 37 08 00 48 c7 44 24 40 00 00 00 00 9c 8f
RSP: 0018:ffffc90002e4f800 EFLAGS: 00000286
RAX: 922e8d27bfbb2300 RBX: 0000000000000000 RCX: 922e8d27bfbb2300
RDX: dffffc0000000000 RSI: ffffffff8a2b3100 RDI: 0000000000000001
RBP: ffffc90002e4f8a0 R08: ffffffff8d89f82f R09: 1ffffffff1b13f05
R10: dffffc0000000000 R11: fffffbfff1b13f06 R12: 0000000000000000
R13: 0000000000000000 R14: dffffc0000000000 R15: 1ffff920005c9f00
 irqentry_exit+0x63/0x70 kernel/entry/common.c:432
 asm_sysvec_reschedule_ipi+0x16/0x20 arch/x86/include/asm/idtentry.h:681
RIP: 0010:netlink_sendmsg+0x68c/0xbe0 net/netlink/af_netlink.c:1897
Code: 11 5c f9 49 89 d8 8b 5c 24 10 49 81 c6 20 05 00 00 4c 89 f0 48 c1 e8 03 42 0f b6 04 28 84 c0 4c 89 44 24 10 0f 85 8c 04 00 00 <45> 8b 36 49 8d 78 34 48 89 f8 48 c1 e8 03 42 0f b6 04 28 84 c0 0f
RSP: 0018:ffffc90002e4f960 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 0000000000000008 RCX: ffff88807d963b80
RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffff88806169b338
RBP: ffffc90002e4fa70 R08: ffff88806169b280 R09: 1ffff110048e315c
R10: dffffc0000000000 R11: ffffed10048e315d R12: 1ffff920005c9f38
R13: dffffc0000000000 R14: ffff88814ce9f520 R15: 0000000000000000
 sock_sendmsg_nosec net/socket.c:706 [inline]
 __sock_sendmsg net/socket.c:718 [inline]
 ____sys_sendmsg+0x5b7/0x8f0 net/socket.c:2445
 ___sys_sendmsg+0x236/0x2e0 net/socket.c:2499
 __sys_sendmsg net/socket.c:2528 [inline]
 __do_sys_sendmsg net/socket.c:2537 [inline]
 __se_sys_sendmsg+0x1af/0x290 net/socket.c:2535
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f94c9a37407
Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007ffe487992b0 EFLAGS: 00000202 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f94c9949880 RCX: 00007f94c9a37407
RDX: 0000000000000000 RSI: 00007ffe48799310 RDI: 0000000000000004
RBP: 000055eaf7ec7f70 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00000000000000bd
R13: 000055eaf7ea79e0 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
vkms_vblank_simulate: vblank timer overrun
----------------
Code disassembly (best guess):
   0:	00 00                	add    %al,(%rax)
   2:	43 c6 44 37 04 f8    	movb   $0xf8,0x4(%r15,%r14,1)
   8:	74 0b                	je     0x15
   a:	0f 0b                	ud2
   c:	48 f7 03 08 00 00 00 	testq  $0x8,(%rbx)
  13:	74 7f                	je     0x94
  15:	bf 01 00 00 00       	mov    $0x1,%edi
  1a:	e8 15 4f 8d f7       	call   0xf78d4f34
  1f:	e8 e0 3e ba f7       	call   0xf7ba3f04
  24:	fb                   	sti
  25:	bf 01 00 00 00       	mov    $0x1,%edi
* 2a:	e8 65 b5 ff ff       	call   0xffffb594 <-- trapping instruction
  2f:	43 c6 44 37 08 00    	movb   $0x0,0x8(%r15,%r14,1)
  35:	48 c7 44 24 40 00 00 	movq   $0x0,0x40(%rsp)
  3c:	00 00
  3e:	9c                   	pushf
  3f:	8f                   	.byte 0x8f