=============================
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
9 locks held by kworker/1:4/4227:
 #0: ffff88806279a138 ((wq_completion)wg-crypt-wg0#5){+.+.}-{0:0}, at: process_one_work+0x760/0x1000 kernel/workqueue.c:-1
 #1: ffffc9000316fd00 ((work_completion)(&peer->transmit_packet_work)){+.+.}-{0:0}, at: process_one_work+0x7a3/0x1000 kernel/workqueue.c:2285
 #2: ffff88807dd6c318 (&peer->endpoint_lock){++-.}-{2:2}, at: wg_socket_send_skb_to_peer+0x50/0x1c0 drivers/net/wireguard/socket.c:173
 #3: ffffffff8c11c7c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
 #4: ffffffff8c11c7c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
 #5: ffffffff8c11c7c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
 #6: ffff888061b02148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: neigh_hh_output include/net/neighbour.h:493 [inline]
 #6: ffff888061b02148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: neigh_output include/net/neighbour.h:507 [inline]
 #6: ffff888061b02148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: ip6_finish_output2+0x1035/0x1500 net/ipv6/ip6_output.c:130
 #7: ffff888061b02108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 #7: ffff888061b02108 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x305/0x4a0 net/sched/sch_generic.c:354
 #8: ffffffff8c11c760 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312

stack backtrace:
CPU: 1 PID: 4227 Comm: kworker/1:4 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: wg-crypt-wg0 wg_packet_tx_worker
Call Trace:
 <TASK>
 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
 cake_dequeue+0x1b8f/0x4aa0 net/sched/sch_cake.c:2199
 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
 __dev_xmit_skb net/core/dev.c:3942 [inline]
 __dev_queue_xmit+0xeb9/0x2ed0 net/core/dev.c:4253
 neigh_hh_output include/net/neighbour.h:493 [inline]
 neigh_output include/net/neighbour.h:507 [inline]
 ip6_finish_output2+0x1035/0x1500 net/ipv6/ip6_output.c:130
 ip6tunnel_xmit include/net/ip6_tunnel.h:160 [inline]
 udp_tunnel6_xmit_skb+0x539/0x9c0 net/ipv6/ip6_udp_tunnel.c:109
 send6+0x54c/0x840 drivers/net/wireguard/socket.c:152
 wg_socket_send_skb_to_peer+0x10d/0x1c0 drivers/net/wireguard/socket.c:178
 wg_packet_create_data_done drivers/net/wireguard/send.c:251 [inline]
 wg_packet_tx_worker+0x1d3/0x790 drivers/net/wireguard/send.c:276
 process_one_work+0x863/0x1000 kernel/workqueue.c:2310
 worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>