=============================
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.0.1358/9321:
 #0: ffff88801ef44d98 (&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: ffff8880763a6148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: net_tx_action+0x73a/0x8e0 net/core/dev.c:5096
 #3: ffff8880763a6108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
 #3: ffff8880763a6108 (&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: 9321 Comm: syz.0.1358 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:__sanitizer_cov_trace_const_cmp4+0x0/0x80 kernel/kcov.c:294
Code: 39 d0 77 22 89 f8 89 f6 48 c7 44 0a 08 03 00 00 00 48 89 44 0a 10 48 89 74 0a 18 4c 89 44 0a 20 49 ff c1 4c 89 09 c3 0f 1f 00 <4c> 8b 04 24 65 48 8b 15 b4 f8 81 7e 65 8b 05 b5 f8 81 7e 25 00 01
RSP: 0018:ffffc900032b7658 EFLAGS: 00000246
RAX: ffffffff88482b98 RBX: 0000000000000000 RCX: 0000000000040000
RDX: ffffc900036ba000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffff884826f4 R09: ffffffff88482f00
R10: 0000000000000000 R11: dffffc0000000001 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 __skb_datagram_iter+0x6e4/0x7c0 net/core/datagram.c:487
 skb_copy_datagram_iter+0xbb/0x210 net/core/datagram.c:541
 skb_copy_datagram_msg include/linux/skbuff.h:3744 [inline]
 __unix_dgram_recvmsg+0x7e3/0x1260 net/unix/af_unix.c:2343
 ____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: 0033:0x7feb8fd29719
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:00007feb8e1a1038 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 00007feb8fee0f80 RCX: 00007feb8fd29719
RDX: 0000000000010106 RSI: 00000000200000c0 RDI: 0000000000000004
RBP: 00007feb8fd9c75e R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007feb8fee0f80 R15: 00007ffdbeefb6a8
 </TASK>
vkms_vblank_simulate: vblank timer overrun
----------------
Code disassembly (best guess):
   0:	39 d0                	cmp    %edx,%eax
   2:	77 22                	ja     0x26
   4:	89 f8                	mov    %edi,%eax
   6:	89 f6                	mov    %esi,%esi
   8:	48 c7 44 0a 08 03 00 	movq   $0x3,0x8(%rdx,%rcx,1)
   f:	00 00
  11:	48 89 44 0a 10       	mov    %rax,0x10(%rdx,%rcx,1)
  16:	48 89 74 0a 18       	mov    %rsi,0x18(%rdx,%rcx,1)
  1b:	4c 89 44 0a 20       	mov    %r8,0x20(%rdx,%rcx,1)
  20:	49 ff c1             	inc    %r9
  23:	4c 89 09             	mov    %r9,(%rcx)
  26:	c3                   	ret
  27:	0f 1f 00             	nopl   (%rax)
* 2a:	4c 8b 04 24          	mov    (%rsp),%r8 <-- trapping instruction
  2e:	65 48 8b 15 b4 f8 81 	mov    %gs:0x7e81f8b4(%rip),%rdx        # 0x7e81f8ea
  35:	7e
  36:	65 8b 05 b5 f8 81 7e 	mov    %gs:0x7e81f8b5(%rip),%eax        # 0x7e81f8f2
  3d:	25                   	.byte 0x25
  3e:	00 01                	add    %al,(%rcx)