INFO: rcu detected stall in mptcp_sendmsg

Status: auto-obsoleted due to no activity on 2026/09/30 00:27
Subsystems: net
Labels: prio:high
[Documentation on labels]
First crash: 105d, last: 105d
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ID Workflow Result Correct Bug Created Started Finished Revision
4a479314 assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ✅ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ✅ VMGuestTrigger: ✅ VMHostTrigger: ❌ ❓ INFO: rcu detected stall in mptcp_sendmsg 2026/07/03 00:46 2026/07/03 00:46 2026/07/03 02:08 93f57954

Sample crash report:
ip6_tunnel: ip6tnl1 xmit: Local address not yet configured!
ip6_tunnel: ip6erspan0 xmit: Local address not yet configured!
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P18209/3:b..l
rcu: 	(detected by 1, t=10503 jiffies, g=109617, q=2238 ncpus=2)
task:syz.0.3216      state:R  running task     stack:24736 pid:18209 tgid:18199 ppid:16311  task_flags:0x400040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5510 [inline]
 __schedule+0x17d9/0x56c0 kernel/sched/core.c:7234
 preempt_schedule_irq+0x4d/0xa0 kernel/sched/core.c:7556
 irqentry_exit_to_kernel_mode include/linux/irq-entry-common.h:539 [inline]
 irqentry_exit+0x14f/0x8f0 kernel/entry/common.c:167
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:should_resched arch/x86/include/asm/preempt.h:104 [inline]
RIP: 0010:__local_bh_enable_ip+0xd8/0x130 kernel/softirq.c:457
Code: 8b e8 6c f4 2b 0a 65 66 8b 05 7c b1 b7 11 66 85 c0 75 32 bf 01 00 00 00 e8 85 f0 0b 00 e8 e0 be 46 00 fb 65 8b 05 58 b1 b7 11 <85> c0 75 05 e8 1f 80 ab ff 5b 41 5e c3 cc cc cc cc cc 90 0f 0b 90
RSP: 0018:ffffc90005edeb28 EFLAGS: 00000202
RAX: 0000000000000000 RBX: 0000000000000200 RCX: 0000000000000046
RDX: 0000000000000006 RSI: ffffffff8dfe0551 RDI: ffffffff8c2a9f80
RBP: ffffc90005edee00 R08: ffffffff9032d3f7 R09: 1ffffffff2065a7e
R10: dffffc0000000000 R11: fffffbfff2065a7f R12: dffffc0000000000
R13: 1ffff92000bdbd88 R14: ffffffff898663db R15: 0000000100088000
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 rcu_read_unlock_bh include/linux/rcupdate.h:914 [inline]
 __dev_queue_xmit+0x1ed7/0x37f0 net/core/dev.c:4907
 NF_HOOK_COND include/linux/netfilter.h:307 [inline]
 ip6_output+0x337/0x540 net/ipv6/ip6_output.c:246
 dst_output include/net/dst.h:471 [inline]
 NF_HOOK include/linux/netfilter.h:318 [inline]
 ip6_xmit+0x117f/0x1a60 net/ipv6/ip6_output.c:379
 inet6_csk_xmit+0x397/0x660 net/ipv6/inet6_connection_sock.c:121
 __tcp_transmit_skb+0x2640/0x47c0 net/ipv4/tcp_output.c:1717
 tcp_transmit_skb net/ipv4/tcp_output.c:1734 [inline]
 tcp_send_syn_data net/ipv4/tcp_output.c:4259 [inline]
 tcp_connect+0x317d/0x53e0 net/ipv4/tcp_output.c:4378
 tcp_sendmsg_fastopen+0x2c5/0x5f0 net/ipv4/tcp.c:1076
 mptcp_sendmsg_fastopen+0x17b/0x540 net/mptcp/protocol.c:1831
 mptcp_sendmsg+0x1a69/0x1d10 net/mptcp/protocol.c:1932
 sock_sendmsg_nosec+0x90/0x180 net/socket.c:775
 __sock_sendmsg net/socket.c:790 [inline]
 ____sys_sendmsg+0x54e/0x850 net/socket.c:2684
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2738
 __sys_sendmmsg+0x273/0x4d0 net/socket.c:2827
 __do_sys_sendmmsg net/socket.c:2854 [inline]
 __se_sys_sendmmsg net/socket.c:2851 [inline]
 __x64_sys_sendmmsg+0xa0/0xc0 net/socket.c:2851
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fdda8d9de59
RSP: 002b:00007fdda9bd4028 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007fdda9026270 RCX: 00007fdda8d9de59
RDX: 0000000000000001 RSI: 000020000000c540 RDI: 0000000000000003
RBP: 00007fdda8e33e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000800 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fdda9026308 R14: 00007fdda9026270 R15: 00007ffc002dfaf8
 </TASK>
rcu: rcu_preempt kthread starved for 3442 jiffies! g109617 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:R  running task     stack:27496 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5510 [inline]
 __schedule+0x17d9/0x56c0 kernel/sched/core.c:7234
 __schedule_loop kernel/sched/core.c:7311 [inline]
 schedule+0x164/0x2b0 kernel/sched/core.c:7326
 schedule_timeout+0x152/0x2c0 kernel/time/sleep_timeout.c:99
 rcu_gp_fqs_loop+0x30c/0x11f0 kernel/rcu/tree.c:2123
 rcu_gp_kthread+0x9e/0x2b0 kernel/rcu/tree.c:2325
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 8233 Comm: kworker/0:8 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Workqueue: wg-crypt-wg0 wg_packet_tx_worker
RIP: 0010:fib6_node_lookup_1+0x8c/0x8b0 net/ipv6/ip6_fib.c:1629
Code: 89 34 24 48 8b 44 24 10 42 80 3c 20 00 74 08 4c 89 f7 e8 d7 3a d0 f7 4d 8b 3e 4c 8d 73 28 4c 89 f0 48 c1 e8 03 42 0f b6 04 20 <84> c0 0f 85 ab 01 00 00 41 0f b7 06 89 c1 80 e1 1f 80 f1 07 bd 01
RSP: 0018:ffffc90000006b98 EFLAGS: 00000a02
RAX: 0000000000000000 RBX: ffff888075de7380 RCX: ffff88807bf83e00
RDX: 0000000000000100 RSI: 0000000000000001 RDI: 0000000000000000
RBP: 0000000000000001 R08: ffffc90000006c6f R09: 0000000000000000
R10: ffffc90000006c60 R11: fffff52000000d8e R12: dffffc0000000000
R13: ffffc90000006c40 R14: ffff888075de73a8 R15: ffffc90000007208
FS:  0000000000000000(0000) GS:ffff888125226000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000020000000c540 CR3: 0000000034684000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 fib6_node_lookup+0xe4/0x1d0 net/ipv6/ip6_fib.c:1701
 fib6_table_lookup+0xbc/0xae0 net/ipv6/route.c:2251
 ip6_pol_route+0x229/0x14d0 net/ipv6/route.c:2292
 pol_lookup_func include/net/ip6_fib.h:668 [inline]
 fib6_rule_lookup+0x222/0x730 net/ipv6/fib6_rules.c:123
 ip6_route_output_flags_noref net/ipv6/route.c:2710 [inline]
 ip6_route_output_flags+0x364/0x5d0 net/ipv6/route.c:2722
 ip6_route_output include/net/ip6_route.h:100 [inline]
 __nf_ip6_route+0x42/0xd0 net/ipv6/netfilter.c:102
 nf_ip6_route include/linux/netfilter_ipv6.h:57 [inline]
 synproxy_send_tcp_ipv6+0x275/0x700 net/netfilter/nf_synproxy_core.c:845
 synproxy_send_client_synack_ipv6+0x83f/0xcd0 net/netfilter/nf_synproxy_core.c:907
 nft_synproxy_eval_v6+0x362/0x4e0 net/netfilter/nft_synproxy.c:90
 nft_synproxy_do_eval+0x3d1/0x550 net/netfilter/nft_synproxy.c:145
 expr_call_ops_eval net/netfilter/nf_tables_core.c:237 [inline]
 nft_do_chain+0x48d/0x1b10 net/netfilter/nf_tables_core.c:285
 nft_do_chain_inet+0x360/0x4b0 net/netfilter/nft_chain_filter.c:162
 nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
 nf_hook_slow+0xc5/0x220 net/netfilter/core.c:619
 nf_hook include/linux/netfilter.h:273 [inline]
 NF_HOOK+0x21f/0x3c0 include/linux/netfilter.h:316
 ip6_input+0x16a/0x270 net/ipv6/ip6_input.c:545
 NF_HOOK+0x336/0x3c0 include/linux/netfilter.h:318
 __netif_receive_skb_one_core net/core/dev.c:6206 [inline]
 __netif_receive_skb net/core/dev.c:6319 [inline]
 process_backlog+0x774/0x1860 net/core/dev.c:6670
 __napi_poll+0xaa/0x330 net/core/dev.c:7729
 napi_poll net/core/dev.c:7792 [inline]
 net_rx_action+0x61d/0xf50 net/core/dev.c:7949
 handle_softirqs+0x225/0x840 kernel/softirq.c:622
 do_softirq+0x76/0xd0 kernel/softirq.c:523
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0xf8/0x130 kernel/softirq.c:450
 wg_socket_send_skb_to_peer+0x16b/0x1d0 drivers/net/wireguard/socket.c:183
 wg_packet_create_data_done drivers/net/wireguard/send.c:251 [inline]
 wg_packet_tx_worker+0x1c8/0x7e0 drivers/net/wireguard/send.c:276
 process_one_work kernel/workqueue.c:3322 [inline]
 process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/02 00:25 net a225f8c20712 27192279 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce INFO: rcu detected stall in mptcp_sendmsg
* Struck through repros no longer work on HEAD.