Patch "net/af_iucv: don't use paged skbs for TX on HiperSockets" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    net/af_iucv: don't use paged skbs for TX on HiperSockets

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     net-af_iucv-don-t-use-paged-skbs-for-tx-on-hipersockets.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From dc5367bcc556e97555fc94a32cd1aadbebdff47e Mon Sep 17 00:00:00 2001
From: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Date: Tue, 10 Jan 2017 17:10:34 +0100
Subject: net/af_iucv: don't use paged skbs for TX on HiperSockets

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


Patches currently in stable-queue which might be from jwi@linux.vnet.ibm.com are

queue-4.9/net-af_iucv-don-t-use-paged-skbs-for-tx-on-hipersockets.patch