linux-kernel - [PATCH 3.2 21/70] xen-netback: don't use last request to determine minimum Tx credit

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Date:	Mon, 18 Jan 2016 03:18:35 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, stable@...r.kernel.org,
	"David Vrabel" <david.vrabel@...rix.com>,
	"Wei Liu" <wei.liu2@...rix.com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>
Subject: [PATCH 3.2 21/70] xen-netback: don't use last request to
 determine minimum Tx credit

3.2.76-rc1 review patch.  If anyone has any objections, please let me know.

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

From: David Vrabel <david.vrabel@...rix.com>

commit 0f589967a73f1f30ab4ac4dd9ce0bb399b4d6357 upstream.

The last from guest transmitted request gives no indication about the
minimum amount of credit that the guest might need to send a packet
since the last packet might have been a small one.

Instead allow for the worst case 128 KiB packet.

This is part of XSA155.

CC: stable@...r.kernel.org
Reviewed-by: Wei Liu <wei.liu2@...rix.com>
Signed-off-by: David Vrabel <david.vrabel@...rix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
[bwh: Backported to 3.2: s/queue/vif/g]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/net/xen-netback/netback.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -864,9 +864,7 @@ static void tx_add_credit(struct xenvif
 	 * Allow a burst big enough to transmit a jumbo packet of up to 128kB.
 	 * Otherwise the interface can seize up due to insufficient credit.
 	 */
-	max_burst = RING_GET_REQUEST(&vif->tx, vif->tx.req_cons)->size;
-	max_burst = min(max_burst, 131072UL);
-	max_burst = max(max_burst, vif->credit_bytes);
+	max_burst = max(131072UL, vif->credit_bytes);
 
 	/* Take care that adding a new chunk of credit doesn't wrap to zero. */
 	max_credit = vif->remaining_credit + vif->credit_bytes;