From nobody Sat Oct 11 09:59:53 2025 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 4E3141B6D06 for ; Fri, 3 Oct 2025 14:01:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759500119; cv=none; b=XtUiIka1tagWn3QB+BJ+yyI+bbyEey17FK1SreoB5A7jQmwCLEoTb2wlFmBb8YaZnWfD3fSzMYu1HeFoL9gNQON09GVPku9qQdFyi2xZLjLlwgYa50tWZoZBcULC003o2rL4CUNtskDhQjEy8B0XeTdYA/ldHJZNq6k80eXF1WE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759500119; c=relaxed/simple; bh=t5EM9sTNa6jp1TsHRTto1TYcoIdeASiDiytfXEu5jjY=; h=From:To:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:content-type; b=suLgMKYT3i5xHHEJiaO8oK5gQrMk28fEzQuOopzjN6AJ8kKCvpAPcpo5kcpxAoA4qikLlkrHnhxG8UYBN62RsUfV6ap7kpIDtXVYw50x/acohnbyBqyCf+GVMbPtjPC3X55WI3hFB/z2J4mG4PiTwdHz9GVcIxvugOjvYuVqoDM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=a8MeNIXy; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="a8MeNIXy" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1759500117; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=TGuG+CeeCwFekLq09ZQq+rY5Zz/Td85BVZSx0qxji1w=; b=a8MeNIXyjGlxb5aNqiYy3y6V7mdSEf5ib8eKSjxs0CNksAWIuxiiaIWrWOR9uo1FtljAbF Hek+ASbZAkdUT5b7mQtZbwk0fmN6H4knsY0u7CJPs9o58Wiq2FfiWwcEJ11j7HF2zQSeKK XuV3D6IKPpqbIwi7YxuizmT1ZXgfotM= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-627-TMMn3YhRNnu5KabwkO-sJg-1; Fri, 03 Oct 2025 10:01:56 -0400 X-MC-Unique: TMMn3YhRNnu5KabwkO-sJg-1 X-Mimecast-MFC-AGG-ID: TMMn3YhRNnu5KabwkO-sJg_1759500115 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 4AE3B180057F for ; Fri, 3 Oct 2025 14:01:55 +0000 (UTC) Received: from gerbillo.redhat.com (unknown [10.44.32.53]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 69D0E1800577 for ; Fri, 3 Oct 2025 14:01:54 +0000 (UTC) From: Paolo Abeni To: mptcp@lists.linux.dev Subject: [PATCH v4 mptcp-next 1/8] mptcp: borrow forward memory from subflow Date: Fri, 3 Oct 2025 16:01:39 +0200 Message-ID: In-Reply-To: References: Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: xPtPCKTvTbt-xewdrLwLKBe38qb5bvVFOMyMrY8mtuw_1759500115 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8"; x-default="true" In the MPTCP receive path, we release the subflow allocated fwd memory just to allocate it again shortly after for the msk. That could increases the failures chances, especially during backlog processing, when other actions could consume the just released memory before the msk socket has a chance to do the rcv allocation. Replace the skb_orphan() call with an open-coded variant that explicitly borrows, with a PAGE_SIZE granularity, the fwd memory from the subflow socket instead of releasing it. During backlog processing the borrowed memory is accounted at release_cb time. Signed-off-by: Paolo Abeni --- v1 -> v2: - rebased - explain why skb_orphan is removed --- net/mptcp/protocol.c | 19 +++++++++++++++---- 1 file changed, 15 insertions(+), 4 deletions(-) diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 574a1e222d9cf..34661ab979158 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -337,11 +337,12 @@ static void mptcp_data_queue_ofo(struct mptcp_sock *m= sk, struct sk_buff *skb) mptcp_rcvbuf_grow(sk); } =20 -static void mptcp_init_skb(struct sock *ssk, - struct sk_buff *skb, int offset, int copy_len) +static int mptcp_init_skb(struct sock *ssk, + struct sk_buff *skb, int offset, int copy_len) { const struct mptcp_subflow_context *subflow =3D mptcp_subflow_ctx(ssk); bool has_rxtstamp =3D TCP_SKB_CB(skb)->has_rxtstamp; + int borrowed; =20 /* the skb map_seq accounts for the skb offset: * mptcp_subflow_get_mapped_dsn() is based on the current tp->copied_seq @@ -357,6 +358,13 @@ static void mptcp_init_skb(struct sock *ssk, =20 skb_ext_reset(skb); skb_dst_drop(skb); + + /* "borrow" the fwd memory from the subflow, instead of reclaiming it */ + skb->destructor =3D NULL; + borrowed =3D ssk->sk_forward_alloc - sk_unused_reserved_mem(ssk); + borrowed &=3D ~(PAGE_SIZE - 1); + sk_forward_alloc_add(ssk, skb->truesize - borrowed); + return borrowed; } =20 static bool __mptcp_move_skb(struct sock *sk, struct sk_buff *skb) @@ -690,9 +698,12 @@ static bool __mptcp_move_skbs_from_subflow(struct mptc= p_sock *msk, =20 if (offset < skb->len) { size_t len =3D skb->len - offset; + int bmem; =20 - mptcp_init_skb(ssk, skb, offset, len); - skb_orphan(skb); + bmem =3D mptcp_init_skb(ssk, skb, offset, len); + skb->sk =3D NULL; + sk_forward_alloc_add(sk, bmem); + atomic_sub(skb->truesize, &ssk->sk_rmem_alloc); ret =3D __mptcp_move_skb(sk, skb) || ret; seq +=3D len; =20 --=20 2.51.0