============================= 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 8 locks held by syz.3.45/4448: #0: ffff888061580d20 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1694 [inline] #0: ffff888061580d20 (sk_lock-AF_INET6){+.+.}-{0:0}, at: mptcp_stream_connect+0x55/0x950 net/mptcp/protocol.c:3399 #1: ffff8880752e5a60 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1694 [inline] #1: ffff8880752e5a60 (k-sk_lock-AF_INET6){+.+.}-{0:0}, at: inet_stream_connect+0x4d/0xa0 net/ipv4/af_inet.c:735 #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: ffffffff8c11c3c0 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312 #5: ffff88802b8ec148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: neigh_hh_output include/net/neighbour.h:493 [inline] #5: ffff88802b8ec148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: neigh_output include/net/neighbour.h:507 [inline] #5: ffff88802b8ec148 (dev->qdisc_running_key ?: &qdisc_running_key){+...}-{0:0}, at: ip6_finish_output2+0x1035/0x1500 net/ipv6/ip6_output.c:130 #6: ffff88802b8ec108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline] #6: ffff88802b8ec108 (&sch->q.lock){+.-.}-{2:2}, at: sch_direct_xmit+0x305/0x4a0 net/sched/sch_generic.c:354 #7: ffffffff8c11c360 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311 stack backtrace: CPU: 1 PID: 4448 Comm: syz.3.45 Not tainted 5.15.189-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 Call Trace: 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:2189 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 dst_output include/net/dst.h:452 [inline] NF_HOOK include/linux/netfilter.h:302 [inline] ip6_xmit+0x1054/0x1670 net/ipv6/ip6_output.c:338 inet6_csk_xmit+0x444/0x6d0 net/ipv6/inet6_connection_sock.c:135 __tcp_transmit_skb+0x1ced/0x31c0 net/ipv4/tcp_output.c:1404 tcp_transmit_skb net/ipv4/tcp_output.c:1422 [inline] tcp_connect+0x21a9/0x4970 net/ipv4/tcp_output.c:3893 tcp_v6_connect+0x1136/0x1920 net/ipv6/tcp_ipv6.c:337 __inet_stream_connect+0x293/0xdf0 net/ipv4/af_inet.c:672 inet_stream_connect+0x62/0xa0 net/ipv4/af_inet.c:736 mptcp_stream_connect+0x674/0x950 net/mptcp/protocol.c:3436 __sys_connect_file net/socket.c:1923 [inline] __sys_connect+0x389/0x410 net/socket.c:1940 __do_sys_connect net/socket.c:1950 [inline] __se_sys_connect net/socket.c:1947 [inline] __x64_sys_connect+0x76/0x80 net/socket.c:1947 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: 0033:0x7f98b493cbe9 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 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:00007f98b2ba4038 EFLAGS: 00000246 ORIG_RAX: 000000000000002a RAX: ffffffffffffffda RBX: 00007f98b4b63fa0 RCX: 00007f98b493cbe9 RDX: 000000000000001c RSI: 0000200000000040 RDI: 0000000000000007 RBP: 00007f98b49bfe19 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f98b4b64038 R14: 00007f98b4b63fa0 R15: 00007fff42d48bb8