[PATCH net v2 1/2] vhost_net: fix ubuf refcount incorrectly when sendmsg fails

[wangyunjian]

From: Yunjian Wang <wangyunj...@huawei.com>

Currently the vhost_zerocopy_callback() maybe be called to decrease
the refcount when sendmsg fails in tun. The error handling in vhost
handle_tx_zerocopy() will try to decrease the same refcount again.
This is wrong. To fix this issue, we only call vhost_net_ubuf_put()
when vq->heads[nvq->desc].len == VHOST_DMA_IN_PROGRESS.

Fixes: 0690899b4d45 ("tun: experimental zero copy tx support")

Signed-off-by: Yunjian Wang <wangyunj...@huawei.com>
---
 drivers/vhost/net.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 531a00d703cd..c8784dfafdd7 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -863,6 +863,7 @@ static void handle_tx_zerocopy(struct vhost_net *net, 
struct socket *sock)
        size_t len, total_len = 0;
        int err;
        struct vhost_net_ubuf_ref *ubufs;
+       struct ubuf_info *ubuf;
        bool zcopy_used;
        int sent_pkts = 0;
 
@@ -895,9 +896,7 @@ static void handle_tx_zerocopy(struct vhost_net *net, 
struct socket *sock)
 
                /* use msg_control to pass vhost zerocopy ubuf info to skb */
                if (zcopy_used) {
-                       struct ubuf_info *ubuf;
                        ubuf = nvq->ubuf_info + nvq->upend_idx;
-
                        vq->heads[nvq->upend_idx].id = cpu_to_vhost32(vq, head);
                        vq->heads[nvq->upend_idx].len = VHOST_DMA_IN_PROGRESS;
                        ubuf->callback = vhost_zerocopy_callback;
@@ -927,7 +926,8 @@ static void handle_tx_zerocopy(struct vhost_net *net, 
struct socket *sock)
                err = sock->ops->sendmsg(sock, &msg, len);
                if (unlikely(err < 0)) {
                        if (zcopy_used) {
-                               vhost_net_ubuf_put(ubufs);
+                               if (vq->heads[ubuf->desc].len == 
VHOST_DMA_IN_PROGRESS)
+                                       vhost_net_ubuf_put(ubufs);
                                nvq->upend_idx = ((unsigned)nvq->upend_idx - 1)
                                        % UIO_MAXIOV;
                        }
-- 
2.23.0