linux-kernel - [PATCH net 2/2] macvtap: handle ubuf refcount correctly when meet erros

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Message-Id: <1480483072-14201-2-git-send-email-jasowang@redhat.com>
Date:   Wed, 30 Nov 2016 13:17:52 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     mst@...hat.com, wangyunjian@...wei.com,
        Jason Wang <jasowang@...hat.com>
Subject: [PATCH net 2/2] macvtap: handle ubuf refcount correctly when meet erros

We trigger uarg->callback() immediately after we decide do datacopy
even if caller want to do zerocopy. This will cause the callback
(vhost_net_zerocopy_callback) decrease the refcount. But when we meet
an error afterwards, the error handling in vhost handle_tx() will try
to decrease it again. This is wrong and fix this by delay the
uarg->callback() until we're sure there's no errors.

Signed-off-by: Jason Wang <jasowang@...hat.com>
---
The patch is needed for -stable.
---
 drivers/net/macvtap.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index bceca28..7869b06 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -742,13 +742,8 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
 
 	if (zerocopy)
 		err = zerocopy_sg_from_iter(skb, from);
-	else {
+	else
 		err = skb_copy_datagram_from_iter(skb, 0, from, len);
-		if (!err && m && m->msg_control) {
-			struct ubuf_info *uarg = m->msg_control;
-			uarg->callback(uarg, false);
-		}
-	}
 
 	if (err)
 		goto err_kfree;
@@ -779,7 +774,11 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
 		skb_shinfo(skb)->destructor_arg = m->msg_control;
 		skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
 		skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG;
+	} else if (m && m->msg_control) {
+		struct ubuf_info *uarg = m->msg_control;
+		uarg->callback(uarg, false);
 	}
+
 	if (vlan) {
 		skb->dev = vlan->dev;
 		dev_queue_xmit(skb);
-- 
2.7.4