[Xenial][Artful][PATCH 2/2] i40e/i40evf: Account for frags split over multiple descriptors in check linearize

[Dan Streetman]

From: Alexander Duyck <alexander.h.duyck at intel.com>

BugLink: http://bugs.launchpad.net/bugs/1723127

The original code for __i40e_chk_linearize didn't take into account the
fact that if a fragment is 16K in size or larger it has to be split over 2
descriptors and the smaller of those 2 descriptors will be on the trailing
edge of the transmit. As a result we can get into situations where we didn't
catch requests that could result in a Tx hang.

This patch takes care of that by subtracting the length of all but the
trailing edge of the stale fragment before we test for sum. By doing this
we can guarantee that we have all cases covered, including the case of a
fragment that spans multiple descriptors. We don't need to worry about
checking the inner portions of this since 12K is the maximum aligned DMA
size and that is larger than any MSS will ever be since the MTU limit for
jumbos is something on the order of 9K.

Signed-off-by: Alexander Duyck <alexander.h.duyck at intel.com>
Tested-by: Andrew Bowers <andrewx.bowers at intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher at intel.com>
(cherry-picked from 248de22e638f10bd5bfc7624a357f940f66ba137)
Signed-off-by: Dan Streetman <ddstreet at canonical.com>

---
Note that this patch applies to Xenial and Artful, but the previous patch
in the series is only required in Xenial.

 drivers/net/ethernet/intel/i40e/i40e_txrx.c   | 26 +++++++++++++++++++++++---
 drivers/net/ethernet/intel/i40evf/i40e_txrx.c | 26 +++++++++++++++++++++++---
 2 files changed, 46 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
index a18c91e33dea..2c83a6ce1b47 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
@@ -2640,10 +2640,30 @@ bool __i40e_chk_linearize(struct sk_buff *skb)
 	/* Walk through fragments adding latest fragment, testing it, and
 	 * then removing stale fragments from the sum.
 	 */
-	stale = &skb_shinfo(skb)->frags[0];
-	for (;;) {
+	for (stale = &skb_shinfo(skb)->frags[0];; stale++) {
+		int stale_size = skb_frag_size(stale);
+
 		sum += skb_frag_size(frag++);
 
+		/* The stale fragment may present us with a smaller
+		 * descriptor than the actual fragment size. To account
+		 * for that we need to remove all the data on the front and
+		 * figure out what the remainder would be in the last
+		 * descriptor associated with the fragment.
+		 */
+		if (stale_size > I40E_MAX_DATA_PER_TXD) {
+			int align_pad = -(stale->page_offset) &
+					(I40E_MAX_READ_REQ_SIZE - 1);
+
+			sum -= align_pad;
+			stale_size -= align_pad;
+
+			do {
+				sum -= I40E_MAX_DATA_PER_TXD_ALIGNED;
+				stale_size -= I40E_MAX_DATA_PER_TXD_ALIGNED;
+			} while (stale_size > I40E_MAX_DATA_PER_TXD);
+		}
+
 		/* if sum is negative we failed to make sufficient progress */
 		if (sum < 0)
 			return true;
@@ -2651,7 +2671,7 @@ bool __i40e_chk_linearize(struct sk_buff *skb)
 		if (!nr_frags--)
 			break;
 
-		sum -= skb_frag_size(stale++);
+		sum -= stale_size;
 	}
 
 	return false;
diff --git a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
index f2163735528d..1f48bcdf1ea5 100644
--- a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
@@ -1843,10 +1843,30 @@ bool __i40evf_chk_linearize(struct sk_buff *skb)
 	/* Walk through fragments adding latest fragment, testing it, and
 	 * then removing stale fragments from the sum.
 	 */
-	stale = &skb_shinfo(skb)->frags[0];
-	for (;;) {
+	for (stale = &skb_shinfo(skb)->frags[0];; stale++) {
+		int stale_size = skb_frag_size(stale);
+
 		sum += skb_frag_size(frag++);
 
+		/* The stale fragment may present us with a smaller
+		 * descriptor than the actual fragment size. To account
+		 * for that we need to remove all the data on the front and
+		 * figure out what the remainder would be in the last
+		 * descriptor associated with the fragment.
+		 */
+		if (stale_size > I40E_MAX_DATA_PER_TXD) {
+			int align_pad = -(stale->page_offset) &
+					(I40E_MAX_READ_REQ_SIZE - 1);
+
+			sum -= align_pad;
+			stale_size -= align_pad;
+
+			do {
+				sum -= I40E_MAX_DATA_PER_TXD_ALIGNED;
+				stale_size -= I40E_MAX_DATA_PER_TXD_ALIGNED;
+			} while (stale_size > I40E_MAX_DATA_PER_TXD);
+		}
+
 		/* if sum is negative we failed to make sufficient progress */
 		if (sum < 0)
 			return true;
@@ -1854,7 +1874,7 @@ bool __i40evf_chk_linearize(struct sk_buff *skb)
 		if (!nr_frags--)
 			break;
 
-		sum -= skb_frag_size(stale++);
+		sum -= stale_size;
 	}
 
 	return false;
-- 
2.15.1