sch_tbf: burst 32855 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.0.238/5098: #0: ffff88802995d520 (sk_lock-AF_INET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1744 [inline] #0: ffff88802995d520 (sk_lock-AF_INET){+.+.}-{0:0}, at: tcp_recvmsg+0x208/0x760 net/ipv4/tcp.c:2565 #1: ffffffff8d11efa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313 #2: ffffffff8d11efa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313 #3: ffffffff8d11f000 (rcu_read_lock_bh){....}-{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: ffff88802584f908 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline] #5: ffff88802584f908 (&sch->q.lock){+.-.}-{2:2}, at: __dev_xmit_skb net/core/dev.c:3925 [inline] #5: ffff88802584f908 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0xa2b/0x2e50 net/core/dev.c:4267 #6: ffffffff8d11efa0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312 stack backtrace: CPU: 1 PID: 5098 Comm: syz.0.238 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/15/2026 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 cake_enqueue+0x5021/0x8270 net/sched/sch_cake.c:1956 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 __tcp_transmit_skb+0x1ca3/0x31e0 net/ipv4/tcp_output.c:1404 tcp_transmit_skb net/ipv4/tcp_output.c:1422 [inline] tcp_write_xmit+0x1a8d/0x65c0 net/ipv4/tcp_output.c:2718 __tcp_push_pending_frames+0x92/0x250 net/ipv4/tcp_output.c:2903 tcp_push_pending_frames include/net/tcp.h:1922 [inline] tcp_data_snd_check net/ipv4/tcp_input.c:5578 [inline] tcp_rcv_established+0xbbd/0x1de0 net/ipv4/tcp_input.c:6075 tcp_v4_do_rcv+0x435/0x9b0 net/ipv4/tcp_ipv4.c:1738 sk_backlog_rcv include/net/sock.h:1080 [inline] __release_sock+0x1e6/0x460 net/core/sock.c:2730 release_sock+0x5b/0x1b0 net/core/sock.c:3273 sk_wait_data+0x203/0x470 net/core/sock.c:2775 tcp_recvmsg_locked+0xe63/0x2690 net/ipv4/tcp.c:2451 tcp_recvmsg+0x22a/0x760 net/ipv4/tcp.c:2566 inet_recvmsg+0x146/0x200 net/ipv4/af_inet.c:868 sock_recvmsg_nosec net/socket.c:969 [inline] sock_recvmsg net/socket.c:987 [inline] __sys_recvfrom+0x396/0x510 net/socket.c:2130 __do_sys_recvfrom net/socket.c:2148 [inline] __se_sys_recvfrom net/socket.c:2144 [inline] __x64_sys_recvfrom+0xda/0xf0 net/socket.c:2144 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: 0033:0x7f5920d38b19 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:00007f591ef6e028 EFLAGS: 00000246 ORIG_RAX: 000000000000002d RAX: ffffffffffffffda RBX: 00007f5920fbf090 RCX: 00007f5920d38b19 RDX: fffffffffffffd0b RSI: 0000200000000340 RDI: 0000000000000004 RBP: 00007f5920dd0b70 R08: 0000000000000000 R09: fffffffffffffd25 R10: 0000000000000720 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f5920fbf128 R14: 00007f5920fbf090 R15: 00007fff5a590a08