=============================
WARNING: suspicious RCU usage
5.15.185-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.0.743/6772:
 #0: ffffffff8c11bfa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312
 #1: ffff88807b4b1148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: net_tx_action+0x6bc/0x870 net/core/dev.c:5128
 #2: ffff88807b4b1108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
 #2: ffff88807b4b1108 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x305/0x4a0 net/sched/sch_generic.c:354
 #3: ffffffff8c11bfa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311

stack backtrace:
CPU: 1 PID: 6772 Comm: syz.0.743 Not tainted 5.15.185-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <IRQ>
 dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
 qdisc_lookup+0xa6/0x650 net/sched/sch_api.c:304
 qdisc_tree_reduce_backlog+0x213/0x4e0 net/sched/sch_api.c:800
 cake_dequeue+0x1b8f/0x4aa0 net/sched/sch_cake.c:2189
 qdisc_peek_dequeued+0x6e/0x1f0 include/net/sch_generic.h:1115
 tbf_dequeue+0x7d/0xce0 net/sched/sch_tbf.c:265
 dequeue_skb net/sched/sch_generic.c:292 [inline]
 qdisc_restart net/sched/sch_generic.c:397 [inline]
 __qdisc_run+0x237/0x1480 net/sched/sch_generic.c:415
 qdisc_run+0x103/0x2f0 include/net/pkt_sched.h:132
 net_tx_action+0x6bc/0x870 net/core/dev.c:5128
 handle_softirqs+0x328/0x820 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x12f/0x220 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:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:169 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x25/0x40 kernel/locking/spinlock.c:202
Code: f6 ff 0f 1f 00 53 48 89 fb 48 83 c7 18 48 8b 74 24 08 e8 8e 9a b1 f7 48 89 df e8 56 6f b2 f7 e8 a1 13 d3 f7 fb bf 01 00 00 00 <e8> 86 93 a6 f7 65 8b 05 27 a3 57 76 85 c0 74 02 5b c3 e8 d4 ad 55
RSP: 0018:ffffc9000338fab0 EFLAGS: 00000282
RAX: c050b61f0be5fa00 RBX: ffff888060e35850 RCX: c050b61f0be5fa00
RDX: dffffc0000000000 RSI: ffffffff8a0b11c0 RDI: 0000000000000001
RBP: ffffc9000338fc78 R08: dffffc0000000000 R09: ffffed100c1c6b0b
R10: ffffed100c1c6b0b R11: 1ffff1100c1c6b0a R12: ffff888021b31dc0
R13: ffff888060e35830 R14: ffff888060e35850 R15: ffff888060e35850
 spin_unlock_irq include/linux/spinlock.h:413 [inline]
 snd_rawmidi_write+0x3d9/0xbc0 sound/core/rawmidi.c:1541
 do_loop_readv_writev fs/read_write.c:-1 [inline]
 do_iter_write+0x3e4/0x7b0 fs/read_write.c:857
 vfs_writev fs/read_write.c:928 [inline]
 do_writev+0x254/0x410 fs/read_write.c:971
 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: 0033:0x7f407bdcc929
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:00007f4079c34038 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00007f407bff3fa0 RCX: 00007f407bdcc929
RDX: 0000000000000002 RSI: 0000200000000840 RDI: 0000000000000004
RBP: 00007f407be4eb39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f407bff3fa0 R15: 00007fff07356f48
 </TASK>
----------------
Code disassembly (best guess):
   0:	f6 ff                	idiv   %bh
   2:	0f 1f 00             	nopl   (%rax)
   5:	53                   	push   %rbx
   6:	48 89 fb             	mov    %rdi,%rbx
   9:	48 83 c7 18          	add    $0x18,%rdi
   d:	48 8b 74 24 08       	mov    0x8(%rsp),%rsi
  12:	e8 8e 9a b1 f7       	call   0xf7b19aa5
  17:	48 89 df             	mov    %rbx,%rdi
  1a:	e8 56 6f b2 f7       	call   0xf7b26f75
  1f:	e8 a1 13 d3 f7       	call   0xf7d313c5
  24:	fb                   	sti
  25:	bf 01 00 00 00       	mov    $0x1,%edi
* 2a:	e8 86 93 a6 f7       	call   0xf7a693b5 <-- trapping instruction
  2f:	65 8b 05 27 a3 57 76 	mov    %gs:0x7657a327(%rip),%eax        # 0x7657a35d
  36:	85 c0                	test   %eax,%eax
  38:	74 02                	je     0x3c
  3a:	5b                   	pop    %rbx
  3b:	c3                   	ret
  3c:	e8                   	.byte 0xe8
  3d:	d4                   	(bad)
  3e:	ad                   	lods   %ds:(%rsi),%eax
  3f:	55                   	push   %rbp