Patch "tun: fix transmit timestamp support" has been added to the 4.7-stable tree

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

tun: fix transmit timestamp support

to the 4.7-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:
tun-fix-transmit-timestamp-support.patch
and it can be found in the queue-4.7 subdirectory.

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

From: Soheil Hassas Yeganeh <[email protected]>
Date: Tue, 23 Aug 2016 18:22:33 -0400
Subject: tun: fix transmit timestamp support

From: Soheil Hassas Yeganeh <[email protected]>

[ Upstream commit 7b996243fab46092fb3a29c773c54be8152366e4 ]

Instead of using sock_tx_timestamp, use skb_tx_timestamp to record software transmit timestamp of a packet.

sock_tx_timestamp resets and overrides the tx_flags of the skb. The function is intended to be called from within the protocol layer when creating the skb, not from a device driver. This is inconsistent with other drivers and will cause issues for TCP.

In TCP, we intend to sample the timestamps for the last byte for each sendmsg/sendpage. For that reason, tcp_sendmsg calls tcp_tx_timestamp only with the last skb that it generates. For example, if a 128KB message is split into two 64KB packets we want to sample the SND timestamp of the last packet. The current code in the tun driver, however, will result in sampling the SND timestamp for both packets.

Also, when the last packet is split into smaller packets for retranmission (see tcp_fragment), the tun driver will record timestamps for all of the retransmitted packets and not only the last packet.

---
 drivers/net/tun.c |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

@@ -878,11 +878,7 @@ static netdev_tx_t tun_net_xmit(struct s
 	if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))
 		goto drop;
 
-	if (skb->sk && sk_fullsock(skb->sk)) {
-		sock_tx_timestamp(skb->sk, skb->sk->sk_tsflags,
-				  &skb_shinfo(skb)->tx_flags);
-		sw_tx_timestamp(skb);
-	}
+	skb_tx_timestamp(skb);
 
 	/* Orphan the skb - required as we might hang on to it
 	 * for indefinite time.

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

queue-4.7/tun-fix-transmit-timestamp-support.patch