sch_tbf: burst 19872 is lower than device lo mtu (65550) ! ============================= 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 7 locks held by syz.1.178/4837: #0: ffff88807920c020 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1744 [inline] #0: ffff88807920c020 (sk_lock-AF_INET6){+.+.}-{0:0}, at: sctp_setsockopt+0x1ec/0xf80 net/sctp/socket.c:4593 #1: ffffffff8c31f320 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313 #2: ffffffff8c31f320 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313 #3: ffffffff8c31f380 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313 #4: ffffffff8c31f380 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313 #5: ffff88807d87a908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline] #5: ffff88807d87a908 (&sch->q.lock){+.-.}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3924 [inline] #5: ffff88807d87a908 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0xa2a/0x2f80 net/core/dev.c:4266 #6: ffffffff8c31f320 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312 stack backtrace: CPU: 1 PID: 4837 Comm: syz.1.178 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026 Call Trace: dump_stack_lvl+0x188/0x250 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:783 cake_enqueue+0x3fe1/0x7fc0 net/sched/sch_cake.c:1964 qdisc_enqueue include/net/sch_generic.h:842 [inline] tbf_enqueue+0x224/0x6e0 net/sched/sch_tbf.c:243 dev_qdisc_enqueue+0x48/0x210 net/core/dev.c:3865 __dev_xmit_skb net/core/dev.c:3949 [inline] __dev_queue_xmit+0xc25/0x2f80 net/core/dev.c:4266 neigh_hh_output include/net/neighbour.h:493 [inline] neigh_output include/net/neighbour.h:507 [inline] ip_finish_output2+0xc87/0x10a0 net/ipv4/ip_output.c:228 NF_HOOK_COND include/linux/netfilter.h:291 [inline] ip_output+0x2c0/0x3e0 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+0x11c1/0x1c00 net/ipv4/ip_output.c:538 sctp_packet_transmit+0x239c/0x2910 net/sctp/output.c:652 sctp_outq_flush_transports net/sctp/outqueue.c:1170 [inline] sctp_outq_flush+0xe62/0x3100 net/sctp/outqueue.c:1218 sctp_cmd_interpreter net/sctp/sm_sideeffect.c:-1 [inline] sctp_side_effects net/sctp/sm_sideeffect.c:1199 [inline] sctp_do_sm+0x4ee2/0x55f0 net/sctp/sm_sideeffect.c:1170 sctp_primitive_REQUESTHEARTBEAT+0x94/0xc0 net/sctp/primitive.c:185 sctp_apply_peer_addr_params+0xde/0x1870 net/sctp/socket.c:2430 sctp_setsockopt_peer_addr_params+0x673/0x940 net/sctp/socket.c:2680 sctp_setsockopt+0x4cd/0xf80 net/sctp/socket.c:4631 __sys_setsockopt+0x2bf/0x3d0 net/socket.c:2212 __do_sys_setsockopt net/socket.c:2223 [inline] __se_sys_setsockopt net/socket.c:2220 [inline] __x64_sys_setsockopt+0xb1/0xc0 net/socket.c:2220 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: 0033:0x7f575ae9ee59 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:00007f57590f8028 EFLAGS: 00000246 ORIG_RAX: 0000000000000036 RAX: ffffffffffffffda RBX: 00007f575b117fa0 RCX: 00007f575ae9ee59 RDX: 0000000000000009 RSI: 0000000000000084 RDI: 0000000000000004 RBP: 00007f575af34d6f R08: 000000000000009c R09: 0000000000000000 R10: 0000200000000840 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f575b118038 R14: 00007f575b117fa0 R15: 00007fff193978e8