linux-kernel - [PATCH 4.9 073/120] net/af_iucv: dont use paged skbs for TX on HiperSockets

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Message-Id: <20170118104651.101780405@linuxfoundation.org>
Date:   Wed, 18 Jan 2017 11:46:31 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Julian Wiedmann <jwi@...ux.vnet.ibm.com>,
        Ursula Braun <ubraun@...ux.vnet.ibm.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.9 073/120] net/af_iucv: dont use paged skbs for TX on HiperSockets

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Julian Wiedmann <jwi@...ux.vnet.ibm.com>

commit dc5367bcc556e97555fc94a32cd1aadbebdff47e upstream.

With commit e53743994e21
("af_iucv: use paged SKBs for big outbound messages"),
we transmit paged skbs for both of AF_IUCV's transport modes
(IUCV or HiperSockets).
The qeth driver for Layer 3 HiperSockets currently doesn't
support NETIF_F_SG, so these skbs would just be linearized again
by the stack.
Avoid that overhead by using paged skbs only for IUCV transport.

cc stable, since this also circumvents a significant skb leak when
sending large messages (where the skb then needs to be linearized).

Signed-off-by: Julian Wiedmann <jwi@...ux.vnet.ibm.com>
Signed-off-by: Ursula Braun <ubraun@...ux.vnet.ibm.com>
Fixes: e53743994e21 ("af_iucv: use paged SKBs for big outbound messages")
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/iucv/af_iucv.c |   25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

--- a/net/iucv/af_iucv.c
+++ b/net/iucv/af_iucv.c
@@ -1036,7 +1036,8 @@ static int iucv_sock_sendmsg(struct sock
 {
 	struct sock *sk = sock->sk;
 	struct iucv_sock *iucv = iucv_sk(sk);
-	size_t headroom, linear;
+	size_t headroom = 0;
+	size_t linear;
 	struct sk_buff *skb;
 	struct iucv_message txmsg = {0};
 	struct cmsghdr *cmsg;
@@ -1114,18 +1115,20 @@ static int iucv_sock_sendmsg(struct sock
 	 * this is fine for SOCK_SEQPACKET (unless we want to support
 	 * segmented records using the MSG_EOR flag), but
 	 * for SOCK_STREAM we might want to improve it in future */
-	headroom = (iucv->transport == AF_IUCV_TRANS_HIPER)
-		   ? sizeof(struct af_iucv_trans_hdr) + ETH_HLEN : 0;
-	if (headroom + len < PAGE_SIZE) {
+	if (iucv->transport == AF_IUCV_TRANS_HIPER) {
+		headroom = sizeof(struct af_iucv_trans_hdr) + ETH_HLEN;
 		linear = len;
 	} else {
-		/* In nonlinear "classic" iucv skb,
-		 * reserve space for iucv_array
-		 */
-		if (iucv->transport != AF_IUCV_TRANS_HIPER)
-			headroom += sizeof(struct iucv_array) *
-				    (MAX_SKB_FRAGS + 1);
-		linear = PAGE_SIZE - headroom;
+		if (len < PAGE_SIZE) {
+			linear = len;
+		} else {
+			/* In nonlinear "classic" iucv skb,
+			 * reserve space for iucv_array
+			 */
+			headroom = sizeof(struct iucv_array) *
+				   (MAX_SKB_FRAGS + 1);
+			linear = PAGE_SIZE - headroom;
+		}
 	}
 	skb = sock_alloc_send_pskb(sk, headroom + linear, len - linear,
 				   noblock, &err, 0);