============================= WARNING: suspicious RCU usage 5.15.185-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 8 locks held by ksoftirqd/1/20: #0: ffff8000143311e0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x18/0x54 include/linux/rcupdate.h:311 #1: ffff8000143311e0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x10/0x4c include/linux/rcupdate.h:311 #2: ffff0000d196e0a0 (slock-AF_INET/1){+.-.}-{2:2}, at: tcp_v4_rcv+0x1f2c/0x2718 net/ipv4/tcp_ipv4.c:2137 #3: ffff8000143311e0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x18/0x54 include/linux/rcupdate.h:311 #4: ffff800014331240 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x18/0x54 include/linux/rcupdate.h:311 #5: ffff800014331240 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x18/0x54 include/linux/rcupdate.h:311 #6: ffff0000ce01b908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline] #6: ffff0000ce01b908 (&sch->q.lock){+.-.}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3911 [inline] #6: ffff0000ce01b908 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0x840/0x2800 net/core/dev.c:4253 #7: ffff8000143311e0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x10/0x4c include/linux/rcupdate.h:311 stack backtrace: CPU: 1 PID: 20 Comm: ksoftirqd/1 Not tainted 5.15.185-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025 Call trace: dump_backtrace+0x0/0x43c arch/arm64/kernel/stacktrace.c:152 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:216 __dump_stack+0x30/0x40 lib/dump_stack.c:88 dump_stack_lvl+0xf8/0x160 lib/dump_stack.c:106 dump_stack+0x1c/0x5c lib/dump_stack.c:113 lockdep_rcu_suspicious+0x140/0x198 kernel/locking/lockdep.c:6574 qdisc_lookup+0xc8/0x64c net/sched/sch_api.c:304 qdisc_tree_reduce_backlog+0x204/0x4a0 net/sched/sch_api.c:800 cake_enqueue+0x1a3c/0x681c net/sched/sch_cake.c:1832 cbs_child_enqueue net/sched/sch_cbs.c:95 [inline] cbs_enqueue_soft+0x14c/0x230 net/sched/sch_cbs.c:128 cbs_enqueue+0x54/0x68 net/sched/sch_cbs.c:136 dev_qdisc_enqueue+0x5c/0x2fc net/core/dev.c:3852 __dev_xmit_skb net/core/dev.c:3936 [inline] __dev_queue_xmit+0xfc0/0x2800 net/core/dev.c:4253 dev_queue_xmit+0x24/0x34 net/core/dev.c:4321 neigh_hh_output include/net/neighbour.h:493 [inline] neigh_output include/net/neighbour.h:507 [inline] ip_finish_output2+0xdac/0x1228 net/ipv4/ip_output.c:228 __ip_finish_output+0x1b0/0x448 net/ipv4/ip_output.c:-1 ip_finish_output+0x40/0x218 net/ipv4/ip_output.c:316 NF_HOOK_COND include/linux/netfilter.h:291 [inline] ip_output+0x314/0x414 net/ipv4/ip_output.c:430 dst_output include/net/dst.h:452 [inline] ip_local_out net/ipv4/ip_output.c:126 [inline] __ip_queue_xmit+0xe00/0x18f0 net/ipv4/ip_output.c:532 ip_queue_xmit+0x5c/0x7c net/ipv4/ip_output.c:546 __tcp_transmit_skb+0x17ec/0x2db8 net/ipv4/tcp_output.c:1404 tcp_transmit_skb net/ipv4/tcp_output.c:1422 [inline] tcp_write_xmit+0x12e0/0x4d60 net/ipv4/tcp_output.c:2707 __tcp_push_pending_frames+0x98/0x228 net/ipv4/tcp_output.c:2892 tcp_push_pending_frames include/net/tcp.h:1916 [inline] tcp_data_snd_check net/ipv4/tcp_input.c:5564 [inline] tcp_rcv_established+0xa4c/0x1c84 net/ipv4/tcp_input.c:6060 tcp_v4_do_rcv+0x33c/0xb9c net/ipv4/tcp_ipv4.c:1731 tcp_v4_rcv+0x1f88/0x2718 net/ipv4/tcp_ipv4.c:2143 ip_protocol_deliver_rcu+0x370/0x778 net/ipv4/ip_input.c:204 ip_local_deliver_finish+0x1b8/0x30c net/ipv4/ip_input.c:231 NF_HOOK+0x2c0/0x354 include/linux/netfilter.h:302 ip_local_deliver+0x120/0x194 net/ipv4/ip_input.c:252 dst_input include/net/dst.h:462 [inline] ip_rcv_finish+0x228/0x260 net/ipv4/ip_input.c:447 NF_HOOK+0x2c0/0x354 include/linux/netfilter.h:302 ip_rcv+0x7c/0x9c net/ipv4/ip_input.c:566 __netif_receive_skb_one_core net/core/dev.c:5525 [inline] __netif_receive_skb+0xcc/0x2ac net/core/dev.c:5639 process_backlog+0x3c8/0x744 net/core/dev.c:6516 __napi_poll+0xb4/0x5dc net/core/dev.c:7075 napi_poll net/core/dev.c:7142 [inline] net_rx_action+0x468/0xa08 net/core/dev.c:7232 handle_softirqs+0x344/0xbf0 kernel/softirq.c:576 run_ksoftirqd+0x7c/0x2a0 kernel/softirq.c:943 smpboot_thread_fn+0x4b0/0x920 kernel/smpboot.c:164 kthread+0x374/0x454 kernel/kthread.c:334 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:870