From nobody Fri Apr 3 16:05:02 2026 Received: from canpmsgout01.his.huawei.com (canpmsgout01.his.huawei.com [113.46.200.216]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5680B36C9ED for ; Tue, 24 Mar 2026 08:27:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=113.46.200.216 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774340889; cv=none; b=rDuL7FdBBKb1B03oiHokU4NfpH3yjRAQvYgB4FgSRpnUyh501eHpeNFzhZSZ3a0rdWqnM3P7QcuCygBWcAPlw/lLFOfQWcerbMrGPQEuVUHEGOd5m5HZt0esyGGBcPMRj7r2ygUNzDCL8ylu5ZZrY2wLHLBMYox8CkwKm/vO3cs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774340889; c=relaxed/simple; bh=5OmiqRxWiKh0ez82OpMgvuHil+XNZD/gFxvFPhrYaRM=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=pmGjFUokL7odGOe6MeW2QwLNyUNi9jZ1f8GFA7lG/U/3emVY+lPtFhdddSwfzUpTdEytXz4Mptc5ti4KXAzr1hxKtdu5jwx+VkFdY91kG2BhSpnC0bFfCeKiw0JH3qGFCNDcPVwihJd0RbGzalyFXYvc/QUT+XR/QqO6bHl0yME= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b=PR1mkROC; arc=none smtp.client-ip=113.46.200.216 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b="PR1mkROC" dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=k7LVUOAVZGg1oxOaM2rw3QIxJxXLJ8+38eC7I9YTytk=; b=PR1mkROCMmgFSYOIS6Zd9PHKq6UmgWPJH1lswZJQOIbpNMN9+ruKikjz9VBBIwjRZmJRu0i1Z 3W7Gmn4syyq9x3iRmO7ZIal+qRCWMyPxFsl1hrEiNN7IcOcgIWxopDaoESrEsA/SH6Pj3HiaCnx Tu0dBKeknlL0IFiEN1t/m0c= Received: from mail.maildlp.com (unknown [172.19.163.104]) by canpmsgout01.his.huawei.com (SkyGuard) with ESMTPS id 4fg31Z1l5Zz1T4KL; Tue, 24 Mar 2026 16:22:26 +0800 (CST) Received: from kwepemj500018.china.huawei.com (unknown [7.202.194.48]) by mail.maildlp.com (Postfix) with ESMTPS id D07964056A; Tue, 24 Mar 2026 16:27:55 +0800 (CST) Received: from huawei.com (10.50.85.128) by kwepemj500018.china.huawei.com (7.202.194.48) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Tue, 24 Mar 2026 16:27:55 +0800 From: Li Xiasong To: Matthieu Baerts , Mat Martineau , Geliang Tang , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman CC: , , , , , Subject: [PATCH net v2] mptcp: fix soft lockup in mptcp_recvmsg() Date: Tue, 24 Mar 2026 16:51:31 +0800 Message-ID: <20260324085131.4187473-1-lixiasong1@huawei.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: kwepems500002.china.huawei.com (7.221.188.17) To kwepemj500018.china.huawei.com (7.202.194.48) Content-Type: text/plain; charset="utf-8" syzbot reported a soft lockup in mptcp_recvmsg() [0]. When receiving data with MSG_PEEK | MSG_WAITALL flags, the skb is not removed from the sk_receive_queue. This causes sk_wait_data() to always find available data and never perform actual waiting, leading to a soft lockup. Fix this by adding a 'last' parameter to track the last peeked skb. This allows sk_wait_data() to make informed waiting decisions and prevent infinite loops when MSG_PEEK is used. [0]: watchdog: BUG: soft lockup - CPU#2 stuck for 156s! [server:1963] Modules linked in: CPU: 2 UID: 0 PID: 1963 Comm: server Not tainted 6.19.0-rc8 #61 PREEMPT(non= e) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/= 2014 RIP: 0010:sk_wait_data+0x15/0x190 Code: 80 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f = 1e fa 41 56 41 55 41 54 49 89 f4 55 48 89 d5 53 48 89 fb <48> 83 ec 30 65 4= 8 8b 05 17 a4 6b 01 48 89 44 24 28 31 c0 65 48 8b RSP: 0018:ffffc90000603ca0 EFLAGS: 00000246 RAX: 0000000000000000 RBX: ffff888102bf0800 RCX: 0000000000000001 RDX: 0000000000000000 RSI: ffffc90000603d18 RDI: ffff888102bf0800 RBP: 0000000000000000 R08: 0000000000000002 R09: 0000000000000101 R10: 0000000000000000 R11: 0000000000000075 R12: ffffc90000603d18 R13: ffff888102bf0800 R14: ffff888102bf0800 R15: 0000000000000000 FS: 00007f6e38b8c4c0(0000) GS:ffff8881b877e000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000055aa7bff1680 CR3: 0000000105cbe000 CR4: 00000000000006f0 Call Trace: mptcp_recvmsg+0x547/0x8c0 net/mptcp/protocol.c:2329 inet_recvmsg+0x11f/0x130 net/ipv4/af_inet.c:891 sock_recvmsg+0x94/0xc0 net/socket.c:1100 __sys_recvfrom+0xb2/0x130 net/socket.c:2256 __x64_sys_recvfrom+0x1f/0x30 net/socket.c:2267 do_syscall_64+0x59/0x2d0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x76/0x7e arch/x86/entry/entry_64.S:131 RIP: 0033:0x7f6e386a4a1d Code: 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 8d 05 f1 de 2c 00 41 89 ca = 8b 00 85 c0 75 20 45 31 c9 45 31 c0 b8 2d 00 00 00 0f 05 <48> 3d 00 f0 ff f= f 77 6b f3 c3 66 0f 1f 84 00 00 00 00 00 41 56 41 RSP: 002b:00007ffc3c4bb078 EFLAGS: 00000246 ORIG_RAX: 000000000000002d RAX: ffffffffffffffda RBX: 000000000000861e RCX: 00007f6e386a4a1d RDX: 00000000000003ff RSI: 00007ffc3c4bb150 RDI: 0000000000000004 RBP: 00007ffc3c4bb570 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000103 R11: 0000000000000246 R12: 00005605dbc00be0 R13: 00007ffc3c4bb650 R14: 0000000000000000 R15: 0000000000000000 Fixes: 612f71d7328c ("mptcp: fix possible stall on recvmsg()") Signed-off-by: Li Xiasong Reviewed-by: Matthieu Baerts (NGI0) --- v1->v2: Thanks to Matthieu Baerts for the suggestion and review. - Move 'last' variable definition into the while loop in mptcp_recvmsg() to narrow its scope. - In __mptcp_recvmsg_mskq(), assign 'last' right after 'copied' is updated, regardless of MSG_PEEK flag. v1: https://lore.kernel.org/netdev/20260302052651.1466983-1-lixiasong1@huawei.c= om/ --- net/mptcp/protocol.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index cf1852b99963..401fb2b17685 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -2006,7 +2006,7 @@ static void mptcp_eat_recv_skb(struct sock *sk, struc= t sk_buff *skb) static int __mptcp_recvmsg_mskq(struct sock *sk, struct msghdr *msg, size_t len, int flags, int copied_total, struct scm_timestamping_internal *tss, - int *cmsg_flags) + int *cmsg_flags, struct sk_buff **last) { struct mptcp_sock *msk =3D mptcp_sk(sk); struct sk_buff *skb, *tmp; @@ -2048,6 +2048,7 @@ static int __mptcp_recvmsg_mskq(struct sock *sk, stru= ct msghdr *msg, } =20 copied +=3D count; + *last =3D skb; =20 if (!(flags & MSG_PEEK)) { msk->bytes_consumed +=3D count; @@ -2288,10 +2289,12 @@ static int mptcp_recvmsg(struct sock *sk, struct ms= ghdr *msg, size_t len, cmsg_flags =3D MPTCP_CMSG_INQ; =20 while (copied < len) { + struct sk_buff *last =3D skb_peek_tail(&sk->sk_receive_queue); int err, bytes_read; =20 bytes_read =3D __mptcp_recvmsg_mskq(sk, msg, len - copied, flags, - copied, &tss, &cmsg_flags); + copied, &tss, &cmsg_flags, + &last); if (unlikely(bytes_read < 0)) { if (!copied) copied =3D bytes_read; @@ -2343,7 +2346,7 @@ static int mptcp_recvmsg(struct sock *sk, struct msgh= dr *msg, size_t len, =20 pr_debug("block timeout %ld\n", timeo); mptcp_cleanup_rbuf(msk, copied); - err =3D sk_wait_data(sk, &timeo, NULL); + err =3D sk_wait_data(sk, &timeo, last); if (err < 0) { err =3D copied ? : err; goto out_err; --=20 2.34.1