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Commit df69491b authored by David S. Miller's avatar David S. Miller
Browse files

Merge branch 'xen-netback' 



Paul Durrant says:

====================
xen-netback: fix rx slot estimation

Sander Eikelenboom reported an issue with ring overflow in netback in
3.14-rc3. This turns outo be be because of a bug in the ring slot estimation
code. This patch series fixes the slot estimation, fixes the BUG_ON() that
was supposed to catch the issue that Sander ran into and also makes a small
fix to start_new_rx_buffer().

v3:
 - Added a cap of MAX_SKB_FRAGS to estimate in patch #2

v2:
 - Added BUG_ON() to patch #1
 - Added more explanation to patch #3
====================

Reported-By: default avatarSander Eikelenboom <linux@eikelenboom.it>
Tested-By: default avatarSander Eikelenboom <linux@eikelenboom.it>
Acked-by: default avatarIan Campbell <ian.campbell@citrix.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parents 49d8137a 1425c7a4

drivers/net/xen-netback/netback.c

+29 −4
Original line number Diff line number Diff line
@@ -192,8 +192,8 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head) 
	 * into multiple copies tend to give large frags their

	 * own buffers as before.

	 */

	if ((offset + size > MAX_BUFFER_OFFSET) &&

	    (size <= MAX_BUFFER_OFFSET) && offset && !head)

	BUG_ON(size > MAX_BUFFER_OFFSET);

	if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)

		return true;



	return false;
@@ -482,6 +482,8 @@ static void xenvif_rx_action(struct xenvif *vif) 


	while ((skb = skb_dequeue(&vif->rx_queue)) != NULL) {

		RING_IDX max_slots_needed;

		RING_IDX old_req_cons;

		RING_IDX ring_slots_used;

		int i;



		/* We need a cheap worse case estimate for the number of
@@ -493,9 +495,28 @@ static void xenvif_rx_action(struct xenvif *vif) 
						PAGE_SIZE);

		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {

			unsigned int size;

			unsigned int offset;



			size = skb_frag_size(&skb_shinfo(skb)->frags[i]);

			max_slots_needed += DIV_ROUND_UP(size, PAGE_SIZE);

			offset = skb_shinfo(skb)->frags[i].page_offset;



			/* For a worse-case estimate we need to factor in

			 * the fragment page offset as this will affect the

			 * number of times xenvif_gop_frag_copy() will

			 * call start_new_rx_buffer().

			 */

			max_slots_needed += DIV_ROUND_UP(offset + size,

							 PAGE_SIZE);

		}



		/* To avoid the estimate becoming too pessimal for some

		 * frontends that limit posted rx requests, cap the estimate

		 * at MAX_SKB_FRAGS.

		 */

		if (max_slots_needed > MAX_SKB_FRAGS)

			max_slots_needed = MAX_SKB_FRAGS;



		/* We may need one more slot for GSO metadata */

		if (skb_is_gso(skb) &&

		   (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4 ||

		    skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6))
@@ -511,8 +532,12 @@ static void xenvif_rx_action(struct xenvif *vif) 
			vif->rx_last_skb_slots = 0;



		sco = (struct skb_cb_overlay *)skb->cb;



		old_req_cons = vif->rx.req_cons;

		sco->meta_slots_used = xenvif_gop_skb(skb, &npo);

		BUG_ON(sco->meta_slots_used > max_slots_needed);

		ring_slots_used = vif->rx.req_cons - old_req_cons;



		BUG_ON(ring_slots_used > max_slots_needed);



		__skb_queue_tail(&rxq, skb);

	}