=============================
WARNING: suspicious RCU usage
5.15.189-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
7 locks held by syz-executor/5177:
 #0: ffffffff8c11c360 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311
 #1: ffffc90000007be0 ((&d->timer)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:45 [inline]
 #1: ffffc90000007be0 ((&d->timer)){+.-.}-{0:0}, at: call_timer_fn+0xbb/0x530 kernel/time/timer.c:1441
 #2: ffffffff8c11c360 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311
 #3: ffffffff8c11c3c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312
 #4: ffff888061c1a108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
 #4: ffff888061c1a108 (&sch->q.lock){+.-.}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3911 [inline]
 #4: ffff888061c1a108 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0xb8a/0x2ed0 net/core/dev.c:4253
 #5: ffff888061c1a148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: tipc_l2_send_msg+0x30a/0x3c0 net/tipc/bearer.c:518
 #6: ffffffff8c11c360 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311

stack backtrace:
CPU: 0 PID: 5177 Comm: syz-executor Not tainted 5.15.189-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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+0x190/0x430 net/sched/sch_api.c:793
 fq_codel_enqueue+0x101a/0x1590 net/sched/sch_fq_codel.c:243
 qdisc_enqueue include/net/sch_generic.h:832 [inline]
 netem_dequeue+0xd39/0x1400 net/sched/sch_netem.c:737
 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
 __dev_xmit_skb net/core/dev.c:3942 [inline]
 __dev_queue_xmit+0xeb9/0x2ed0 net/core/dev.c:4253
 tipc_l2_send_msg+0x30a/0x3c0 net/tipc/bearer.c:518
 tipc_bearer_xmit_skb+0x292/0x3c0 net/tipc/bearer.c:577
 tipc_disc_timeout+0x568/0x6b0 net/tipc/discover.c:338
 call_timer_fn+0x16c/0x530 kernel/time/timer.c:1451
 expire_timers kernel/time/timer.c:1496 [inline]
 __run_timers+0x525/0x7c0 kernel/time/timer.c:1767
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1780
 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:lock_acquire+0x1fb/0x3f0 kernel/locking/lockdep.c:5627
Code: f6 84 24 81 00 00 00 02 0f 85 f6 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 <66> 43 c7 44 3d 09 00 00 43 c6 44 3d 0b 00 65 48 8b 04 25 28 00 00
RSP: 0018:ffffc90003aafd60 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 66e0252ccdf89200
RDX: 0000000000000000 RSI: ffffffff8a0b2860 RDI: ffffffff8a599340
RBP: ffffc90003aafe70 R08: dffffc0000000000 R09: fffffbfff1ff6e19
R10: fffffbfff1ff6e19 R11: 1ffffffff1ff6e18 R12: ffffffff8c11c360
R13: 1ffff92000755fb8 R14: 0000000000000246 R15: dffffc0000000000
 rcu_lock_acquire+0x2a/0x30 include/linux/rcupdate.h:312
 rcu_read_lock include/linux/rcupdate.h:739 [inline]
 __task_pid_nr_ns+0x21/0x420 kernel/pid.c:497
 task_pid_vnr include/linux/sched.h:1533 [inline]
 __do_sys_setpgid kernel/sys.c:1066 [inline]
 __se_sys_setpgid+0x72/0x650 kernel/sys.c:1058
 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: 0033:0x7fdc072c9787
Code: 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 6d 00 00 00 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:00007ffeab5ec1f8 EFLAGS: 00000246 ORIG_RAX: 000000000000006d
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fdc072c9787
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007ffeab5ec23c R08: 0000000000000000 R09: 00007fdc07ff46c0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000021
R13: 00000000000927c0 R14: 000000000001baf1 R15: 00007ffeab5ec290
 </TASK>
----------------
Code disassembly (best guess):
   0:	f6 84 24 81 00 00 00 	testb  $0x2,0x81(%rsp)
   7:	02
   8:	0f 85 f6 00 00 00    	jne    0x104
   e:	41 f7 c6 00 02 00 00 	test   $0x200,%r14d
  15:	74 01                	je     0x18
  17:	fb                   	sti
  18:	48 c7 44 24 60 0e 36 	movq   $0x45e0360e,0x60(%rsp)
  1f:	e0 45
  21:	4b c7 44 3d 00 00 00 	movq   $0x0,0x0(%r13,%r15,1)
  28:	00 00
* 2a:	66 43 c7 44 3d 09 00 	movw   $0x0,0x9(%r13,%r15,1) <-- trapping instruction
  31:	00
  32:	43 c6 44 3d 0b 00    	movb   $0x0,0xb(%r13,%r15,1)
  38:	65                   	gs
  39:	48                   	rex.W
  3a:	8b                   	.byte 0x8b
  3b:	04 25                	add    $0x25,%al
  3d:	28 00                	sub    %al,(%rax)