============================= 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 8 locks held by syz.0.1473/9565: #0: ffff88805e9d8120 (sk_lock-AF_INET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1744 [inline] #0: ffff88805e9d8120 (sk_lock-AF_INET){+.+.}-{0:0}, at: l2tp_ip_sendmsg+0x30/0x1440 net/l2tp/l2tp_ip.c:405 #1: ffffffff8d11efa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312 #2: ffffffff8d11efa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313 #3: ffffffff8d11efa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313 #4: ffffffff8d11f000 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313 #5: ffffffff8d11f000 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313 #6: ffff888072841908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline] #6: ffff888072841908 (&sch->q.lock){+.-.}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3925 [inline] #6: ffff888072841908 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0xa2b/0x2e50 net/core/dev.c:4267 #7: ffffffff8d11efa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312 stack backtrace: CPU: 0 PID: 9565 Comm: syz.0.1473 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026 Call Trace: 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 sfq_enqueue+0x14ad/0x2260 net/sched/sch_sfq.c:-1 qdisc_enqueue include/net/sch_generic.h:844 [inline] tbf_enqueue+0x225/0x6e0 net/sched/sch_tbf.c:243 dev_qdisc_enqueue+0x48/0x210 net/core/dev.c:3866 __dev_xmit_skb net/core/dev.c:3950 [inline] __dev_queue_xmit+0xbde/0x2e50 net/core/dev.c:4267 neigh_hh_output include/net/neighbour.h:493 [inline] neigh_output include/net/neighbour.h:507 [inline] ip_finish_output2+0xc77/0x10e0 net/ipv4/ip_output.c:228 NF_HOOK_COND include/linux/netfilter.h:291 [inline] ip_output+0x2ba/0x3e0 net/ipv4/ip_output.c:434 dst_output include/net/dst.h:452 [inline] ip_local_out net/ipv4/ip_output.c:126 [inline] __ip_queue_xmit+0x11fc/0x1c60 net/ipv4/ip_output.c:538 l2tp_ip_sendmsg+0x567/0x1440 net/l2tp/l2tp_ip.c:498 sock_sendmsg_nosec net/socket.c:706 [inline] __sock_sendmsg net/socket.c:718 [inline] ____sys_sendmsg+0x5be/0x8f0 net/socket.c:2446 ___sys_sendmsg+0x236/0x2e0 net/socket.c:2500 __sys_sendmmsg+0x2ba/0x500 net/socket.c:2586 __do_sys_sendmmsg net/socket.c:2615 [inline] __se_sys_sendmmsg net/socket.c:2612 [inline] __x64_sys_sendmmsg+0x9c/0xb0 net/socket.c:2612 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: 0033:0x7fcb75589559 Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fcb737e0028 EFLAGS: 00000246 ORIG_RAX: 0000000000000133 RAX: ffffffffffffffda RBX: 00007fcb7580ffa0 RCX: 00007fcb75589559 RDX: 00000000040000cf RSI: 0000200000000900 RDI: 0000000000000005 RBP: 00007fcb75620b20 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007fcb75810038 R14: 00007fcb7580ffa0 R15: 00007ffea05de128