net_ratelimit: 50 callbacks suppressed
=============================
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
4 locks held by syz.7.1983/17688:
 #0: 
ffffffff8d11efa0 (
rcu_read_lock
){....}-{1:2}
, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
 #1: ffff888064e5b148
 (dev->qdisc_running_key ?: &qdisc_running_key
){+..-}-{0:0}
, at: net_tx_action+0x6d9/0x880 net/core/dev.c:5155
 #2: ffff888064e5b108
 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x301/0x4a0 net/sched/sch_generic.c:357
 #3: ffffffff8d11efa0
 (rcu_read_lock
){....}-{1:2}
, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312

stack backtrace:
CPU: 0 PID: 17688 Comm: syz.7.1983 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/15/2026
Call Trace:
 <TASK>
 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+0x52/0xc0 arch/x86/kernel/apic/apic.c:1108
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0033:0x7f9c60407d7c
Code: 8b 76 f8 48 39 f2 73 13 66 0f 1f 44 00 00 48 8b 70 f8 48 83 e8 08 48 39 f2 72 f3 48 39 c3 73 3e 48 89 33 48 89 c6 48 83 c3 08 <48> 89 08 48 8b 0b 48 8b 55 00 eb c0 48 39 f2 72 a4 48 39 f0 0f 83
RSP: 002b:00007fff1d2d5a80 EFLAGS: 00000202
RAX: 00007f9c5fc01ab0 RBX: 00007f9c5fc01938 RCX: ffffffff83e88e84
RDX: ffffffff83e88e84 RSI: 00007f9c5fc01ab0 RDI: 00007f9c5fc019f0
RBP: 00007f9c5fc01900 R08: 00007f9c607a8000 R09: 00007f9c607be128
R10: 0000000000000003 R11: ffffffff819fffff R12: 00007f9c5fc01ae0
R13: 0000000000000012 R14: 000000000000003c R15: 0000000000000003
 </TASK>