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Date: Mon, 28 Jun 2010 10:11:43 -0700
From: Sridhar Samudrala <sri@...ibm.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Sridhar Samudrala <samudrala@...ibm.com>,
Arnd Bergmann <arnd@...db.de>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Juan Quintela <quintela@...hat.com>,
Rusty Russell <rusty@...tcorp.com.au>, Jes.Sorensen@...hat.com,
kraxel@...hat.com,
Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>,
kvm@...r.kernel.org, virtualization@...ts.osdl.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vhost: break out of polling loop on error
On Sun, 2010-06-27 at 11:59 +0300, Michael S. Tsirkin wrote:
> When ring parsing fails, we currently handle this
> as ring empty condition. This means that we enable
> kicks and recheck ring empty: if this not empty,
> we re-start polling which of course will fail again.
>
> Instead, let's return a negative error code and stop polling.
One minor comment on error return below. With that change,
Acked-by: Sridhar Samudrala <sri@...ibm.com>
>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>
> Dave, I'm sending this out so it can get reviewed.
> I'll put this on my vhost tree
> so no need for you to pick this patch directly.
>
> drivers/vhost/net.c | 12 ++++++++++--
> drivers/vhost/vhost.c | 33 +++++++++++++++++----------------
> drivers/vhost/vhost.h | 8 ++++----
> 3 files changed, 31 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 0f41c91..54096ee 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -98,7 +98,8 @@ static void tx_poll_start(struct vhost_net *net, struct socket *sock)
> static void handle_tx(struct vhost_net *net)
> {
> struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX];
> - unsigned head, out, in, s;
> + unsigned out, in, s;
> + int head;
> struct msghdr msg = {
> .msg_name = NULL,
> .msg_namelen = 0,
> @@ -135,6 +136,9 @@ static void handle_tx(struct vhost_net *net)
> ARRAY_SIZE(vq->iov),
> &out, &in,
> NULL, NULL);
> + /* On error, stop handling until the next kick. */
> + if (head < 0)
> + break;
> /* Nothing new? Wait for eventfd to tell us they refilled. */
> if (head == vq->num) {
> wmem = atomic_read(&sock->sk->sk_wmem_alloc);
> @@ -192,7 +196,8 @@ static void handle_tx(struct vhost_net *net)
> static void handle_rx(struct vhost_net *net)
> {
> struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_RX];
> - unsigned head, out, in, log, s;
> + unsigned out, in, log, s;
> + int head;
> struct vhost_log *vq_log;
> struct msghdr msg = {
> .msg_name = NULL,
> @@ -228,6 +233,9 @@ static void handle_rx(struct vhost_net *net)
> ARRAY_SIZE(vq->iov),
> &out, &in,
> vq_log, &log);
> + /* On error, stop handling until the next kick. */
> + if (head < 0)
> + break;
> /* OK, now we need to know about added descriptors. */
> if (head == vq->num) {
> if (unlikely(vhost_enable_notify(vq))) {
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 3b83382..5ccd384 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -873,12 +873,13 @@ static unsigned get_indirect(struct vhost_dev *dev, struct vhost_virtqueue *vq,
> * number of output then some number of input descriptors, it's actually two
> * iovecs, but we pack them into one and note how many of each there were.
> *
> - * This function returns the descriptor number found, or vq->num (which
> - * is never a valid descriptor number) if none was found. */
> -unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
> - struct iovec iov[], unsigned int iov_size,
> - unsigned int *out_num, unsigned int *in_num,
> - struct vhost_log *log, unsigned int *log_num)
> + * This function returns the descriptor number found, or vq->num (which is
> + * never a valid descriptor number) if none was found. A negative code is
> + * returned on error. */
> +int vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
> + struct iovec iov[], unsigned int iov_size,
> + unsigned int *out_num, unsigned int *in_num,
> + struct vhost_log *log, unsigned int *log_num)
> {
> struct vring_desc desc;
> unsigned int i, head, found = 0;
> @@ -890,13 +891,13 @@ unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
> if (get_user(vq->avail_idx, &vq->avail->idx)) {
> vq_err(vq, "Failed to access avail idx at %p\n",
> &vq->avail->idx);
> - return vq->num;
> + return -EFAULT;
> }
>
> if ((u16)(vq->avail_idx - last_avail_idx) > vq->num) {
> vq_err(vq, "Guest moved used index from %u to %u",
> last_avail_idx, vq->avail_idx);
> - return vq->num;
> + return -EFAULT;
This should be -EINVAL
> }
>
> /* If there's nothing new since last we looked, return invalid. */
> @@ -912,14 +913,14 @@ unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
> vq_err(vq, "Failed to read head: idx %d address %p\n",
> last_avail_idx,
> &vq->avail->ring[last_avail_idx % vq->num]);
> - return vq->num;
> + return -EFAULT;
> }
>
> /* If their number is silly, that's an error. */
> if (head >= vq->num) {
> vq_err(vq, "Guest says index %u > %u is available",
> head, vq->num);
> - return vq->num;
> + return -EINVAL;
> }
>
> /* When we start there are none of either input nor output. */
> @@ -933,19 +934,19 @@ unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
> if (i >= vq->num) {
> vq_err(vq, "Desc index is %u > %u, head = %u",
> i, vq->num, head);
> - return vq->num;
> + return -EINVAL;
> }
> if (++found > vq->num) {
> vq_err(vq, "Loop detected: last one at %u "
> "vq size %u head %u\n",
> i, vq->num, head);
> - return vq->num;
> + return -EINVAL;
> }
> ret = copy_from_user(&desc, vq->desc + i, sizeof desc);
> if (ret) {
> vq_err(vq, "Failed to get descriptor: idx %d addr %p\n",
> i, vq->desc + i);
> - return vq->num;
> + return -EFAULT;
> }
> if (desc.flags & VRING_DESC_F_INDIRECT) {
> ret = get_indirect(dev, vq, iov, iov_size,
> @@ -954,7 +955,7 @@ unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
> if (ret < 0) {
> vq_err(vq, "Failure detected "
> "in indirect descriptor at idx %d\n", i);
> - return vq->num;
> + return ret;
> }
> continue;
> }
> @@ -964,7 +965,7 @@ unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
> if (ret < 0) {
> vq_err(vq, "Translation failure %d descriptor idx %d\n",
> ret, i);
> - return vq->num;
> + return ret;
> }
> if (desc.flags & VRING_DESC_F_WRITE) {
> /* If this is an input descriptor,
> @@ -981,7 +982,7 @@ unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
> if (*in_num) {
> vq_err(vq, "Descriptor has out after in: "
> "idx %d\n", i);
> - return vq->num;
> + return -EINVAL;
> }
> *out_num += ret;
> }
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index 44591ba..11ee13d 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -120,10 +120,10 @@ long vhost_dev_ioctl(struct vhost_dev *, unsigned int ioctl, unsigned long arg);
> int vhost_vq_access_ok(struct vhost_virtqueue *vq);
> int vhost_log_access_ok(struct vhost_dev *);
>
> -unsigned vhost_get_vq_desc(struct vhost_dev *, struct vhost_virtqueue *,
> - struct iovec iov[], unsigned int iov_count,
> - unsigned int *out_num, unsigned int *in_num,
> - struct vhost_log *log, unsigned int *log_num);
> +int vhost_get_vq_desc(struct vhost_dev *, struct vhost_virtqueue *,
> + struct iovec iov[], unsigned int iov_count,
> + unsigned int *out_num, unsigned int *in_num,
> + struct vhost_log *log, unsigned int *log_num);
> void vhost_discard_vq_desc(struct vhost_virtqueue *);
>
> int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len);
--
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