From nobody Sun Jul 5 05:55:33 2026 Received: from sender4-of-o54.zoho.com (sender4-of-o54.zoho.com [136.143.188.54]) (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 3EAE12FB965 for ; Wed, 17 Jun 2026 06:48:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=pass smtp.client-ip=136.143.188.54 ARC-Seal: i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781678936; cv=pass; b=o2IuHvw5XDFsnvhYrNRSQuFgdgwmtOrd4wOVVsHAnQ+EdrwB1isT8PRmeXVrI+klxvawiV1WHtZpFhoZuDkdSZu4YWwWsZkGtW22Kl0xZxkf2XRNffjKqubvC/4W3SyllUuadREwCo+ziu5lUFxcBArIm59ofKvr+0BniN/I0jQ= ARC-Message-Signature: i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781678936; c=relaxed/simple; bh=6OwEqVN6lf35BJN+fTiwjdOSrfyql/UJbfA5RPfoudQ=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=KQBRhLa0uCxdDT74vUEKvelWjqkc2Kj892tN4j3USC6xw7oztj8zZNjW/HJmxMiH1mk8HBHBldGjLdmovpP0PFrtdI5d70H8gv1l0ifd8c3fLUpMCMcWL4PvLrkxDPfYSGhXVfNIUETjEEb6P6lbkKFgSakzVq66+r3swiTvtp4= ARC-Authentication-Results: i=2; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=mpiricsoftware.com; spf=pass smtp.mailfrom=mpiricsoftware.com; dkim=fail (0-bit key) header.d=mpiricsoftware.com header.i=kalpan.jani@mpiricsoftware.com header.b=OxfXp+Yl reason="key not found in DNS"; arc=pass smtp.client-ip=136.143.188.54 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=mpiricsoftware.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=mpiricsoftware.com Authentication-Results: smtp.subspace.kernel.org; dkim=fail reason="key not found in DNS" (0-bit key) header.d=mpiricsoftware.com header.i=kalpan.jani@mpiricsoftware.com header.b="OxfXp+Yl" ARC-Seal: i=1; a=rsa-sha256; t=1781678927; cv=none; d=zohomail.com; s=zohoarc; b=JqkxQ2GmMFLqN/J8zCzPZD07wNDi6B46HemImu/s97OcKFGGJX4b3s2vwSiRDuQi+HeNo4GV5vRM2hSCDfYBnMv+O14K7oNZTC8leUWfmsoMwZabGDFqs1YCkNqyLmkj5CxCn/8/u5xWcijwNqqjWlmx8qIG28KWPRcOqveAT8M= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1781678927; h=Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:MIME-Version:Message-ID:Subject:Subject:To:To:Message-Id:Reply-To; bh=IvPz2L3JpD1Hv1qlFe7Z9E5ArwwK/Di7HDN9uM7Vv9c=; b=L3Q2zb8AgJ45O33/GmM0E42FbPHKS6rppLoydW76FODeoBzwYFy3HYUlYhYUeVBjRj063wQqU7d90DJOgu0gaRGsq19oi+X4o4QI/REklZDiSoxFLB+GFhCj4Lp5mJx5X2mmvVFqYpnDBhy9Ee4TFRairadySX0iP5y0+spB5jE= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass header.i=mpiricsoftware.com; spf=pass smtp.mailfrom=kalpan.jani@mpiricsoftware.com; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1781678927; s=mpiric; d=mpiricsoftware.com; i=kalpan.jani@mpiricsoftware.com; h=From:From:To:To:Cc:Cc:Subject:Subject:Date:Date:Message-ID:MIME-Version:Content-Transfer-Encoding:Message-Id:Reply-To; bh=IvPz2L3JpD1Hv1qlFe7Z9E5ArwwK/Di7HDN9uM7Vv9c=; b=OxfXp+YlsAFu7/ouOiJgHf8dDxq7KWqCI+IkIQD3Zr7VlK1/sxUZglSbKB9wGhoZ aekfoAKwYlAtCVE8GDUfQaGNAFBsCQLgR5eRdvyHZZWMs2XYVSS79hDGeLIJ9GRQeZy wOPj0yWLPOh5SWOloUHQNyw6P5S6QxTdr+SMqD3g= Received: by mx.zohomail.com with SMTPS id 1781678924784932.396867762129; Tue, 16 Jun 2026 23:48:44 -0700 (PDT) From: Kalpan Jani To: mptcp@lists.linux.dev Cc: matttbe@kernel.org, martineau@kernel.org, pabeni@redhat.com, shardul.b@mpiricsoftware.com, janak@mpiric.us, kalpanjani009@gmail.com, akshit@mpiricsoftware.com, Kalpan Jani , syzbot+fb2c3fa2ba28aec94627@syzkaller.appspotmail.com Subject: [PATCH mptcp-next] mptcp: fix lockdep splat in mptcp_subflow_create_socket Date: Wed, 17 Jun 2026 12:18:35 +0530 Message-ID: <20260617064835.2957303-1-kalpan.jani@mpiricsoftware.com> X-Mailer: git-send-email 2.43.0 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-ZohoMailClient: External Content-Type: text/plain; charset="utf-8" Move sk_net_refcnt_upgrade() outside the socket lock to avoid GFP_KERNEL allocation under lock_sock_nested(), which can trigger page reclaim and create a circular locking dependency detected by lockdep. The circular dependency chain detected: fs_reclaim --> sk_lock-AF_INET --> k-sk_lock-AF_INET/1 This operation is safe after lock release since the socket is fully initialized and no other references to it exist yet. Tested with mptcp/mptcp-upstream-virtme-docker CI: all 24 tests pass. Fixes: 0cafd77dcd03 ("net: add a refcount tracker for kernel sockets") Reported-by: syzbot+fb2c3fa2ba28aec94627@syzkaller.appspotmail.com Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/599 Signed-off-by: Kalpan Jani --- net/mptcp/subflow.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c index 8e386899ceb9..0dc8d32ef291 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -1800,11 +1800,6 @@ int mptcp_subflow_create_socket(struct sock *sk, uns= igned short family, /* the newly created socket has to be in the same cgroup as its parent */ mptcp_attach_cgroup(sk, sf->sk); =20 - /* kernel sockets do not by default acquire net ref, but TCP timer - * needs it. - * Update ns_tracker to current stack trace and refcounted tracker. - */ - sk_net_refcnt_upgrade(sf->sk); err =3D tcp_set_ulp(sf->sk, "mptcp"); if (err) goto err_free; @@ -1812,6 +1807,11 @@ int mptcp_subflow_create_socket(struct sock *sk, uns= igned short family, mptcp_sockopt_sync_locked(mptcp_sk(sk), sf->sk); release_sock(sf->sk); =20 + /* Upgrade net namespace refcount after releasing the socket lock + * to avoid GFP_KERNEL allocation under lock (lockdep: fs_reclaim). + */ + sk_net_refcnt_upgrade(sf->sk); + /* the newly created socket really belongs to the owning MPTCP * socket, even if for additional subflows the allocation is performed * by a kernel workqueue. Adjust inode references, so that the --=20 2.43.0