=============================
WARNING: suspicious RCU usage
5.15.174-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 ksoftirqd/1/20:
 #0: ffffc90000da7a80 ((&peer->hb_timer)){+.-.}-{0:0}, at: lockdep_copy_map include/linux/lockdep.h:45 [inline]
 #0: ffffc90000da7a80 ((&peer->hb_timer)){+.-.}-{0:0}, at: call_timer_fn+0xbe/0x560 kernel/time/timer.c:1441
 #1: ffff88814c806ca0 (slock-AF_INET6){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
 #1: ffff88814c806ca0 (slock-AF_INET6){+.-.}-{2:2}, at: sctp_generate_heartbeat_event+0x8c/0x450 net/sctp/sm_sideeffect.c:371
 #2: ffffffff8cb1fd20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312
 #3: ffffffff8cb1fd80 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312
 #4: ffffffff8cb1fd80 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312
 #5: ffff888020326908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline]
 #5: ffff888020326908 (&sch->q.lock){+.-.}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3879 [inline]
 #5: ffff888020326908 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0xc1f/0x32b0 net/core/dev.c:4221
 #6: ffffffff8cb1fd20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311

stack backtrace:
CPU: 1 PID: 20 Comm: ksoftirqd/1 Not tainted 5.15.174-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/25/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e3/0x2d0 lib/dump_stack.c:106
 qdisc_lookup+0xa8/0x630 net/sched/sch_api.c:304
 qdisc_tree_reduce_backlog+0x212/0x4f0 net/sched/sch_api.c:800
 pfifo_tail_enqueue+0x2ca/0x400 net/sched/sch_fifo.c:51
 qdisc_enqueue include/net/sch_generic.h:832 [inline]
 tbf_enqueue+0x35d/0x6f0 net/sched/sch_tbf.c:243
 dev_qdisc_enqueue+0x47/0x240 net/core/dev.c:3820
 __dev_xmit_skb net/core/dev.c:3904 [inline]
 __dev_queue_xmit+0xe32/0x32b0 net/core/dev.c:4221
 neigh_hh_output include/net/neighbour.h:493 [inline]
 neigh_output include/net/neighbour.h:507 [inline]
 ip_finish_output2+0xcd7/0x11a0 net/ipv4/ip_output.c:228
 dst_output include/net/dst.h:443 [inline]
 ip_local_out net/ipv4/ip_output.c:126 [inline]
 __ip_queue_xmit+0x12df/0x1d90 net/ipv4/ip_output.c:532
 sctp_packet_transmit+0x2565/0x2b70 net/sctp/output.c:652
 sctp_outq_flush_transports net/sctp/outqueue.c:1170 [inline]
 sctp_outq_flush+0x13c7/0x3d70 net/sctp/outqueue.c:1218
 sctp_side_effects net/sctp/sm_sideeffect.c:1199 [inline]
 sctp_do_sm+0x55e7/0x5c80 net/sctp/sm_sideeffect.c:1170
 sctp_generate_heartbeat_event+0x321/0x450 net/sctp/sm_sideeffect.c:391
 call_timer_fn+0x16d/0x560 kernel/time/timer.c:1451
 expire_timers kernel/time/timer.c:1496 [inline]
 __run_timers+0x67c/0x890 kernel/time/timer.c:1767
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1780
 handle_softirqs+0x3a7/0x930 kernel/softirq.c:558
 run_ksoftirqd+0xc6/0x120 kernel/softirq.c:925
 smpboot_thread_fn+0x51b/0x9d0 kernel/smpboot.c:164
 kthread+0x3f6/0x4f0 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>