From: Jason Wang <jasowang@redhat.com>
Date: Wed, 12 Sep 2018 11:17:02 +0800
Subject: tuntap: simplify error handling in tun_build_skb()
Patch-mainline: v4.20-rc1
Git-commit: f7053b6ccb65a36fdfed6ad92b808464839f0eb6
References: bsc#1109837

There's no need to duplicate page get logic in each action. So this
patch tries to get page and calculate the offset before processing XDP
actions (except for XDP_DROP), and undo them when meet errors (we
don't care the performance on errors). This will be used for factoring
out XDP logic.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/net/tun.c |   10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1656,17 +1656,13 @@ static struct sk_buff *tun_build_skb(str
 			xdp_do_flush_map();
 			if (err)
 				goto err_redirect;
-			rcu_read_unlock();
-			local_bh_enable();
-			return NULL;
+			goto out;
 		case XDP_TX:
 			get_page(alloc_frag->page);
 			alloc_frag->offset += buflen;
 			if (tun_xdp_tx(tun->dev, &xdp) < 0)
 				goto err_redirect;
-			rcu_read_unlock();
-			local_bh_enable();
-			return NULL;
+			goto out;
 		case XDP_PASS:
 			delta = orig_data - xdp.data;
 			len = xdp.data_end - xdp.data;
@@ -1697,7 +1693,7 @@ static struct sk_buff *tun_build_skb(str
 
 err_redirect:
 	put_page(alloc_frag->page);
-err_xdp:
+out:
 	rcu_read_unlock();
 	local_bh_enable();
 	this_cpu_inc(tun->pcpu_stats->rx_dropped);