=============================
WARNING: suspicious RCU usage
5.15.173-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
5 locks held by syz.0.275/5330:
 #0: ffff888079467d98 (&u->iolock){+.+.}-{3:3}, at: __unix_dgram_recvmsg+0x24d/0x1260 net/unix/af_unix.c:2301
 #1: ffffffff8c91fc60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312
 #2: ffff8880611a0148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: net_tx_action+0x73a/0x8e0 net/core/dev.c:5096
 #3: ffff8880611a0108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
 #3: ffff8880611a0108 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x370/0x5e0 net/sched/sch_generic.c:354
 #4: ffffffff8c91fc60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311

stack backtrace:
CPU: 0 PID: 5330 Comm: syz.0.275 Not tainted 5.15.173-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e3/0x2d0 lib/dump_stack.c:106
 qdisc_lookup+0xa8/0x630 net/sched/sch_api.c:304
 qdisc_tree_reduce_backlog+0x212/0x4f0 net/sched/sch_api.c:800
 codel_qdisc_dequeue+0x1546/0x21d0 net/sched/sch_codel.c:102
 qdisc_peek_dequeued+0x6f/0x220 include/net/sch_generic.h:1100
 tbf_dequeue+0x80/0xd60 net/sched/sch_tbf.c:259
 dequeue_skb net/sched/sch_generic.c:292 [inline]
 qdisc_restart net/sched/sch_generic.c:397 [inline]
 __qdisc_run+0x253/0x1e90 net/sched/sch_generic.c:415
 qdisc_run+0x10d/0x320 include/net/pkt_sched.h:132
 net_tx_action+0x73a/0x8e0 net/core/dev.c:5096
 handle_softirqs+0x3a7/0x930 kernel/softirq.c:558
 __do_softirq kernel/softirq.c:592 [inline]
 invoke_softirq kernel/softirq.c:432 [inline]
 __irq_exit_rcu+0x157/0x240 kernel/softirq.c:641
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:653
 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_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xd4/0x130 kernel/locking/spinlock.c:194
Code: 9c 8f 44 24 20 42 80 3c 23 00 74 08 4c 89 f7 e8 d2 44 8c f7 f6 44 24 21 02 75 4e 41 f7 c7 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> 77 75 19 f7 65 8b 05 98 68 c4 75 85 c0 74 3f 48 c7 04 24 0e 36
RSP: 0018:ffffc900031575a0 EFLAGS: 00000206
RAX: 8ccceae6779c5f00 RBX: 1ffff9200062aeb8 RCX: ffffffff81632d68
RDX: dffffc0000000000 RSI: ffffffff8a8b2a80 RDI: 0000000000000001
RBP: ffffc90003157630 R08: dffffc0000000000 R09: fffffbfff20ec837
R10: 0000000000000000 R11: dffffc0000000001 R12: dffffc0000000000
R13: 1ffff9200062aeb4 R14: ffffc900031575c0 R15: 0000000000000246
 spin_unlock_irqrestore include/linux/spinlock.h:418 [inline]
 __wake_up_common_lock kernel/sched/wait.c:140 [inline]
 __wake_up_sync_key+0x121/0x1c0 kernel/sched/wait.c:205
 __unix_dgram_recvmsg+0x5fe/0x1260 net/unix/af_unix.c:2331
 ____sys_recvmsg+0x286/0x530
 ___sys_recvmsg+0x1ec/0x690 net/socket.c:2697
 do_recvmmsg+0x36f/0x8f0 net/socket.c:2791
 __sys_recvmmsg net/socket.c:2870 [inline]
 __do_sys_recvmmsg net/socket.c:2893 [inline]
 __se_sys_recvmmsg net/socket.c:2886 [inline]
 __x64_sys_recvmmsg+0x195/0x240 net/socket.c:2886
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f9afc27f759
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f9afa6d6038 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 00007f9afc437058 RCX: 00007f9afc27f759
RDX: 0000000000010106 RSI: 00000000200000c0 RDI: 0000000000000004
RBP: 00007f9afc2f275e R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f9afc437058 R15: 00007ffe93037f68
 </TASK>
vkms_vblank_simulate: vblank timer overrun
----------------
Code disassembly (best guess):
   0:	9c                   	pushf
   1:	8f 44 24 20          	pop    0x20(%rsp)
   5:	42 80 3c 23 00       	cmpb   $0x0,(%rbx,%r12,1)
   a:	74 08                	je     0x14
   c:	4c 89 f7             	mov    %r14,%rdi
   f:	e8 d2 44 8c f7       	call   0xf78c44e6
  14:	f6 44 24 21 02       	testb  $0x2,0x21(%rsp)
  19:	75 4e                	jne    0x69
  1b:	41 f7 c7 00 02 00 00 	test   $0x200,%r15d
  22:	74 01                	je     0x25
  24:	fb                   	sti
  25:	bf 01 00 00 00       	mov    $0x1,%edi
* 2a:	e8 77 75 19 f7       	call   0xf71975a6 <-- trapping instruction
  2f:	65 8b 05 98 68 c4 75 	mov    %gs:0x75c46898(%rip),%eax        # 0x75c468ce
  36:	85 c0                	test   %eax,%eax
  38:	74 3f                	je     0x79
  3a:	48                   	rex.W
  3b:	c7                   	.byte 0xc7
  3c:	04 24                	add    $0x24,%al
  3e:	0e                   	(bad)
  3f:	36                   	ss