=============================
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
5 locks held by syz.2.984/7914:
 #0: ffff888079685da0 (&u->iolock){+.+.}-{3:3}, at: __unix_dgram_recvmsg+0x1f8/0xd50 net/unix/af_unix.c:2312
 #1: ffffffff8d11efa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
 #2: ffff88805dacf948 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: net_tx_action+0x6d9/0x880 net/core/dev.c:5155
 #3: ffff88805dacf908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 #3: ffff88805dacf908 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x301/0x4a0 net/sched/sch_generic.c:357
 #4: ffffffff8d11efa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312

stack backtrace:
CPU: 1 PID: 7914 Comm: syz.2.984 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026
Call Trace:
 <IRQ>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 qdisc_lookup+0xa6/0x640 net/sched/sch_api.c:304
 qdisc_tree_reduce_backlog+0x188/0x480 net/sched/sch_api.c:800
 fq_codel_dequeue_drop net/sched/sch_fq_codel.c:326 [inline]
 fq_codel_peek+0x1dd/0x330 net/sched/sch_fq_codel.c:358
 tbf_dequeue+0x7b/0xcf0 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+0x22f/0x14b0 net/sched/sch_generic.c:418
 qdisc_run+0x103/0x2f0 include/net/pkt_sched.h:132
 net_tx_action+0x6d9/0x880 net/core/dev.c:5155
 handle_softirqs+0x336/0x830 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_count arch/x86/include/asm/preempt.h:27 [inline]
RIP: 0010:preempt_latency_start kernel/sched/core.c:5489 [inline]
RIP: 0010:preempt_schedule_common+0x25/0xd0 kernel/sched/core.c:6570
Code: 00 00 0f 1f 00 41 57 41 56 53 49 bf 00 00 00 00 00 fc ff df eb 0d 48 f7 03 08 00 00 00 0f 84 a6 00 00 00 65 ff 05 e3 58 31 76 <65> 8b 05 dc 58 31 76 25 ff ff ff 7f 83 f8 01 75 42 48 8b 5c 24 18
RSP: 0018:ffffc900049974e0 EFLAGS: 00000202
RAX: dffffc0000000004 RBX: 1ffff92000932ea0 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: ffffffff8a2b2b60 RDI: 00000000ffffffff
RBP: ffffc90004997578 R08: ffffffff91046177 R09: 1ffffffff2208c2e
R10: dffffc0000000000 R11: fffffbfff2208c2f R12: dffffc0000000000
R13: 0000000000000000 R14: dffffc0000000000 R15: dffffc0000000000
 preempt_schedule+0xbc/0xd0 kernel/sched/core.c:6596
 preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:34
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
 _raw_spin_unlock_irqrestore+0x10d/0x120 kernel/locking/spinlock.c:194
 spin_unlock_irqrestore include/linux/spinlock.h:419 [inline]
 __wake_up_common_lock kernel/sched/wait.c:140 [inline]
 __wake_up_sync_key+0x128/0x190 kernel/sched/wait.c:205
 __unix_dgram_recvmsg+0x4b1/0xd50 net/unix/af_unix.c:2342
 ____sys_recvmsg+0x2ca/0x5b0 net/socket.c:-1
 ___sys_recvmsg+0x213/0x5c0 net/socket.c:2707
 do_recvmmsg+0x360/0x7f0 net/socket.c:2801
 __sys_recvmmsg net/socket.c:2880 [inline]
 __do_sys_recvmmsg net/socket.c:2903 [inline]
 __se_sys_recvmmsg net/socket.c:2896 [inline]
 __x64_sys_recvmmsg+0x195/0x250 net/socket.c:2896
 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: 0033:0x7f86a6d20559
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:00007f86a4f56028 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 00007f86a6fa7090 RCX: 00007f86a6d20559
RDX: 0000000000010106 RSI: 00002000000000c0 RDI: 0000000000000004
RBP: 00007f86a6db7b20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f86a6fa7128 R14: 00007f86a6fa7090 R15: 00007fff118f9038
 </TASK>
----------------
Code disassembly (best guess):
   0:	00 00                	add    %al,(%rax)
   2:	0f 1f 00             	nopl   (%rax)
   5:	41 57                	push   %r15
   7:	41 56                	push   %r14
   9:	53                   	push   %rbx
   a:	49 bf 00 00 00 00 00 	movabs $0xdffffc0000000000,%r15
  11:	fc ff df
  14:	eb 0d                	jmp    0x23
  16:	48 f7 03 08 00 00 00 	testq  $0x8,(%rbx)
  1d:	0f 84 a6 00 00 00    	je     0xc9
  23:	65 ff 05 e3 58 31 76 	incl   %gs:0x763158e3(%rip)        # 0x7631590d
* 2a:	65 8b 05 dc 58 31 76 	mov    %gs:0x763158dc(%rip),%eax        # 0x7631590d <-- trapping instruction
  31:	25 ff ff ff 7f       	and    $0x7fffffff,%eax
  36:	83 f8 01             	cmp    $0x1,%eax
  39:	75 42                	jne    0x7d
  3b:	48 8b 5c 24 18       	mov    0x18(%rsp),%rbx