=============================
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.4.317/5558:
 #0: ffff888076184da0 (&u->iolock){+.+.}-{3:3}, at: __unix_dgram_recvmsg+0x1f8/0xd50 net/unix/af_unix.c:2312
 #1: ffffffff8c31ef60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
 #2: ffff888025da3148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: net_tx_action+0x6d9/0x880 net/core/dev.c:5154
 #3: ffff888025da3108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 #3: ffff888025da3108 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x301/0x4a0 net/sched/sch_generic.c:357
 #4: ffffffff8c31ef60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312

stack backtrace:
CPU: 1 PID: 5558 Comm: syz.4.317 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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:783
 cake_dequeue+0x1ddf/0x4a50 net/sched/sch_cake.c:2201
 qdisc_peek_dequeued+0x6e/0x1f0 include/net/sch_generic.h:1125
 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:131
 net_tx_action+0x6d9/0x880 net/core/dev.c:5154
 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:lock_acquire+0x208/0x400 kernel/locking/lockdep.c:5627
Code: f7 84 24 80 00 00 00 00 02 00 00 43 c6 44 3d 04 f8 0f 85 f1 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 44 3d 00 00 00 00 00 43 c7 44 3d 08 00 00 00 00 65 48 8b 04
RSP: 0018:ffffc9000151f4a0 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 02f8735a0c80f500
RDX: 0000000000000000 RSI: ffffffff8a2b3e80 RDI: ffffffff8a7a4280
RBP: ffffc9000151f5a8 R08: dffffc0000000000 R09: 1ffffffff203de2e
R10: dffffc0000000000 R11: fffffbfff203de2f R12: ffff888076184da0
R13: 1ffff920002a3ea0 R14: 0000000000000246 R15: dffffc0000000000
 __mutex_lock_common+0x1e5/0x2400 kernel/locking/mutex.c:596
 __mutex_lock kernel/locking/mutex.c:729 [inline]
 mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
 __unix_dgram_recvmsg+0x1f8/0xd50 net/unix/af_unix.c:2312
 ____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: 0033:0x7fe73ebf80d9
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:00007fe73ce2f028 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 00007fe73ee80090 RCX: 00007fe73ebf80d9
RDX: 0000000000010106 RSI: 00002000000000c0 RDI: 0000000000000003
RBP: 00007fe73ec8f024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe73ee80128 R14: 00007fe73ee80090 R15: 00007ffdee0638d8
 </TASK>
----------------
Code disassembly (best guess):
   0:	f7 84 24 80 00 00 00 	testl  $0x200,0x80(%rsp)
   7:	00 02 00 00
   b:	43 c6 44 3d 04 f8    	movb   $0xf8,0x4(%r13,%r15,1)
  11:	0f 85 f1 00 00 00    	jne    0x108
  17:	41 f7 c6 00 02 00 00 	test   $0x200,%r14d
  1e:	74 01                	je     0x21
  20:	fb                   	sti
  21:	48 c7 44 24 60 0e 36 	movq   $0x45e0360e,0x60(%rsp)
  28:	e0 45
* 2a:	4b c7 44 3d 00 00 00 	movq   $0x0,0x0(%r13,%r15,1) <-- trapping instruction
  31:	00 00
  33:	43 c7 44 3d 08 00 00 	movl   $0x0,0x8(%r13,%r15,1)
  3a:	00 00
  3c:	65                   	gs
  3d:	48                   	rex.W
  3e:	8b                   	.byte 0x8b
  3f:	04                   	.byte 0x4