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Date: Mon, 28 Jun 2010 20:25:59 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Sridhar Samudrala <sri@...ibm.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 Mon, Jun 28, 2010 at 10:11:43AM -0700, Sridhar Samudrala wrote:
> 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>
Right. In fact, we don't really use the return code,
and the generated binary is smaller if we return
-EINVAL always.
So that's what I'll do.
> >
> > 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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