linux-kernel - Re: [syzbot] [mptcp?] WARNING in subflow_data

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Message-ID: <692805b5.a70a0220.d98e3.00f8.GAE@google.com>
Date: Thu, 27 Nov 2025 00:03:01 -0800
From: syzbot <syzbot+0ff6b771b4f7a5bce83b@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, mptcp@...ts.linux.dev, pabeni@...hat.com, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mptcp?] WARNING in subflow_data_ready (4)

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in subflow_data_ready

MPTCP: fallaback under lock 0 req mpc 1 req mpj 0 state 16 parent state 7 send 0 received 0
------------[ cut here ]------------
WARNING: CPU: 1 PID: 23 at net/mptcp/subflow.c:1527 subflow_data_ready+0x59d/0x980 net/mptcp/subflow.c:1527
Modules linked in:
CPU: 1 UID: 0 PID: 23 Comm: ksoftirqd/1 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:subflow_data_ready+0x59d/0x980 net/mptcp/subflow.c:1527
Code: e0 48 c7 c7 c0 71 ee 8c 44 89 f9 8b 54 24 1c 48 c1 ee 02 45 0f b7 c0 83 e6 01 e8 2e 6c 51 f6 48 8b 7c 24 10 e8 44 ee 16 00 90 <0f> 0b 90 58 5a e8 e9 fb 72 f6 48 89 df e8 51 ac ff ff 31 ff 89 c5
RSP: 0018:ffffc900001d7348 EFLAGS: 00010202
RAX: 0000000000000101 RBX: ffff8880343cd940 RCX: 0000000000000002
RDX: 0000000000000000 RSI: ffffffff8da29344 RDI: ffffffff8bf078c0
RBP: ffff8880312b1538 R08: 0000000000000001 R09: 0000000000000001
R10: ffffffff90824bd7 R11: 0000000000000001 R12: ffff8880312b0c00
R13: 1ffff9200003ae70 R14: 0000000000000004 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff888124b0d000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6ced887d58 CR3: 0000000064f00000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 tcp_data_ready+0x110/0x550 net/ipv4/tcp_input.c:5355
 tcp_data_queue+0x1aa6/0x5000 net/ipv4/tcp_input.c:5445
 tcp_rcv_state_process+0xfb6/0x6490 net/ipv4/tcp_input.c:7159
 tcp_v4_do_rcv+0x68e/0x10a0 net/ipv4/tcp_ipv4.c:1954
 tcp_v4_rcv+0x3077/0x4db0 net/ipv4/tcp_ipv4.c:2374
 ip_protocol_deliver_rcu+0xba/0x4c0 net/ipv4/ip_input.c:205
 ip_local_deliver_finish+0x3f2/0x720 net/ipv4/ip_input.c:239
 NF_HOOK include/linux/netfilter.h:318 [inline]
 NF_HOOK include/linux/netfilter.h:312 [inline]
 ip_local_deliver+0x18e/0x1f0 net/ipv4/ip_input.c:260
 dst_input include/net/dst.h:474 [inline]
 ip_rcv_finish net/ipv4/ip_input.c:453 [inline]
 NF_HOOK include/linux/netfilter.h:318 [inline]
 NF_HOOK include/linux/netfilter.h:312 [inline]
 ip_rcv+0x2e0/0x600 net/ipv4/ip_input.c:573
 __netif_receive_skb_one_core+0x197/0x1e0 net/core/dev.c:6079
 __netif_receive_skb+0x1d/0x160 net/core/dev.c:6192
 process_backlog+0x439/0x15e0 net/core/dev.c:6544
 __napi_poll.constprop.0+0xba/0x550 net/core/dev.c:7594
 napi_poll net/core/dev.c:7657 [inline]
 net_rx_action+0x97f/0xef0 net/core/dev.c:7784
 handle_softirqs+0x219/0x8e0 kernel/softirq.c:622
 run_ksoftirqd kernel/softirq.c:1063 [inline]
 run_ksoftirqd+0x3a/0x60 kernel/softirq.c:1055
 smpboot_thread_fn+0x3f7/0xae0 kernel/smpboot.c:160
 kthread+0x3c5/0x780 kernel/kthread.c:463
 ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


Tested on:

commit:         8e621c9a Merge tag 'net-6.18-rc7' of git://git.kernel...
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=14916f42580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=1cd7f786c0f5182f
dashboard link: https://syzkaller.appspot.com/bug?extid=0ff6b771b4f7a5bce83b
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=158f657c580000