sch_tbf: burst 4398 is lower than device lo mtu (65550) ! ============================= WARNING: suspicious RCU usage 5.15.179-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 5 locks held by syz-executor332/4236: #0: ffffffff8cb1f4e0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312 #1: ffffffff8cb1f540 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312 #2: ffffffff8cb1f540 (rcu_read_lock_bh){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:312 #3: ffff8880219d4108 (&sch->q.lock){+...}-{2:2}, at: spin_lock include/linux/spinlock.h:363 [inline] #3: ffff8880219d4108 (&sch->q.lock){+...}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3910 [inline] #3: ffff8880219d4108 (&sch->q.lock){+...}-{2:2}, at: __dev_queue_xmit+0xc1f/0x32b0 net/core/dev.c:4252 #4: ffffffff8cb1f4e0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:311 stack backtrace: CPU: 0 PID: 4236 Comm: syz-executor332 Not tainted 5.15.179-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025 Call Trace: __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x1e3/0x2d0 lib/dump_stack.c:106 qdisc_lookup+0xa8/0x630 net/sched/sch_api.c:304 qdisc_tree_reduce_backlog+0x212/0x4f0 net/sched/sch_api.c:800 fq_codel_enqueue+0x1139/0x15e0 net/sched/sch_fq_codel.c:247 qdisc_enqueue include/net/sch_generic.h:832 [inline] tbf_enqueue+0x35d/0x6f0 net/sched/sch_tbf.c:243 dev_qdisc_enqueue+0x47/0x240 net/core/dev.c:3851 __dev_xmit_skb net/core/dev.c:3935 [inline] __dev_queue_xmit+0xe32/0x32b0 net/core/dev.c:4252 neigh_hh_output include/net/neighbour.h:493 [inline] neigh_output include/net/neighbour.h:507 [inline] ip6_finish_output2+0xead/0x15a0 net/ipv6/ip6_output.c:130 ip6_send_skb+0x1af/0x390 net/ipv6/ip6_output.c:1951 udp_v6_send_skb+0xac4/0x1470 net/ipv6/udp.c:1285 udpv6_sendmsg+0x22ab/0x31d0 net/ipv6/udp.c:1586 sock_sendmsg_nosec net/socket.c:704 [inline] __sock_sendmsg net/socket.c:716 [inline] ____sys_sendmsg+0x59e/0x8f0 net/socket.c:2436 ___sys_sendmsg+0x252/0x2e0 net/socket.c:2490 __sys_sendmmsg+0x2bf/0x560 net/socket.c:2576 __do_sys_sendmmsg net/socket.c:2605 [inline] __se_sys_sendmmsg net/socket.c:2602 [inline] __x64_sys_sendmmsg+0x9c/0xb0 net/socket.c:2602 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x66/0xd0 RIP: 0033:0x7f454ce31869 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f454cdf2218 EFLAGS: 00000246 ORIG_RAX: 0000000000000133 RAX: ffffffffffffffda RBX: 00007f454cebb348 RCX: 00007f454ce31869 RDX: 00000000000004ff RSI: 00002000000092c0 RDI: 0000000000000009 RBP: 00007f454cebb340 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f454ce88074 R13: 00002000000002c8 R14: 00002000000002c0 R15: 00002000000092c0