linux-kernel - [PATCH 3.19.y-ckt 109/160] xen-netback: don't use last request to determine minimum Tx credit

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Message-Id: <1453252038-31915-110-git-send-email-kamal@canonical.com>
Date:	Tue, 19 Jan 2016 17:06:27 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	David Vrabel <david.vrabel@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 109/160] xen-netback: don't use last request to determine minimum Tx credit

3.19.8-ckt13 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

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.

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>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 drivers/net/xen-netback/netback.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 409e296..865a0a40 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -812,9 +812,7 @@ static void tx_add_credit(struct xenvif_queue *queue)
 	 * 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(&queue->tx, queue->tx.req_cons)->size;
-	max_burst = min(max_burst, 131072UL);
-	max_burst = max(max_burst, queue->credit_bytes);
+	max_burst = max(131072UL, queue->credit_bytes);
 
 	/* Take care that adding a new chunk of credit doesn't wrap to zero. */
 	max_credit = queue->remaining_credit + queue->credit_bytes;
-- 
1.9.1