Patch "tg3: Fix for tg3 transmit queue 0 timed out when too many gso_segs" has been added to the 4.4-stable tree

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

tg3: Fix for tg3 transmit queue 0 timed out when too many gso_segs

to the 4.4-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:
tg3-fix-for-tg3-transmit-queue-0-timed-out-when-too-many-gso_segs.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Siva Reddy Kallam <[email protected]>
Date: Wed, 3 Feb 2016 14:09:38 +0530
Subject: tg3: Fix for tg3 transmit queue 0 timed out when too many gso_segs

From: Siva Reddy Kallam <[email protected]>

[ Upstream commit b7d987295c74500b733a0ba07f9a9bcc4074fa83 ]

tg3_tso_bug() can hit a condition where the entire tx ring is not big enough to segment the GSO packet. For example, if MSS is very small, gso_segs can exceed the tx ring size. When we hit the condition, it will cause tx timeout.

tg3_tso_bug() is called to handle TSO and DMA hardware bugs. For TSO bugs, if tg3_tso_bug() cannot succeed, we have to drop the packet. For DMA bugs, we can still fall back to linearize the SKB and let the hardware transmit the TSO packet.

This patch adds a function tg3_tso_bug_gso_check() to check if there are enough tx descriptors for GSO before calling tg3_tso_bug(). The caller will then handle the error appropriately - drop or lineraize the SKB.

v2: Corrected patch description to avoid confusion.

---
 drivers/net/ethernet/broadcom/tg3.c |   25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

@@ -7833,6 +7833,14 @@ static int tigon3_dma_hwbug_workaround(s
 	return ret;
 }
 
+static bool tg3_tso_bug_gso_check(struct tg3_napi *tnapi, struct sk_buff *skb)
+{
+	/* Check if we will never have enough descriptors,
+	 * as gso_segs can be more than current ring size
+	 */
+	return skb_shinfo(skb)->gso_segs < tnapi->tx_pending / 3;
+}
+
 static netdev_tx_t tg3_start_xmit(struct sk_buff *, struct net_device *);
 
 /* Use GSO to workaround all TSO packets that meet HW bug conditions

@@ -7936,14 +7944,19 @@ static netdev_tx_t tg3_start_xmit(struct
 		 * vlan encapsulated.
 		 */
 		if (skb->protocol == htons(ETH_P_8021Q) ||
-		    skb->protocol == htons(ETH_P_8021AD))
-			return tg3_tso_bug(tp, tnapi, txq, skb);
+		    skb->protocol == htons(ETH_P_8021AD)) {
+			if (tg3_tso_bug_gso_check(tnapi, skb))
+				return tg3_tso_bug(tp, tnapi, txq, skb);
+			goto drop;
+		}
 
 		if (!skb_is_gso_v6(skb)) {
 			if (unlikely((ETH_HLEN + hdr_len) > 80) &&
-			    tg3_flag(tp, TSO_BUG))
-				return tg3_tso_bug(tp, tnapi, txq, skb);
-
+			    tg3_flag(tp, TSO_BUG)) {
+				if (tg3_tso_bug_gso_check(tnapi, skb))
+					return tg3_tso_bug(tp, tnapi, txq, skb);
+				goto drop;
+			}
 			ip_csum = iph->check;
 			ip_tot_len = iph->tot_len;
 			iph->check = 0;

@@ -8075,7 +8088,7 @@ static netdev_tx_t tg3_start_xmit(struct
 	if (would_hit_hwbug) {
 		tg3_tx_skb_unmap(tnapi, tnapi->tx_prod, i);
 
-		if (mss) {
+		if (mss && tg3_tso_bug_gso_check(tnapi, skb)) {
 			/* If it's a TSO packet, do GSO instead of
 			 * allocating and copying to a large linear SKB
 			 */

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/tg3-fix-for-tg3-transmit-queue-0-timed-out-when-too-many-gso_segs.patch