[PATCH V3 2/2] vhost: handle polling errors

Jason Wang
2013-01-06T07:18:38Z

Polling errors were ignored by vhost/vhost_net, this may lead to crash when
trying to remove vhost from waitqueue when after the polling is failed. Solve
this problem by:

- checking the poll->wqh before trying to remove from waitqueue
- report an error when poll() returns a POLLERR in vhost_start_poll()
- report an error when vhost_start_poll() fails in
vhost_vring_ioctl()/vhost_net_set_backend() which is used to notify the
failure to userspace.
- report an error in the data path in vhost_net when meet polling errors.

After those changes, we can safely drop the tx polling state in vhost_net since
it was replaced by the checking of poll->wqh.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/vhost/net.c | 74 ++++++++++++++++--------------------------------
drivers/vhost/vhost.c | 31 +++++++++++++++-----
drivers/vhost/vhost.h | 2 +-
3 files changed, 49 insertions(+), 58 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index d10ad6f..125c1e5 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -64,20 +64,10 @@ enum {
VHOST_NET_VQ_MAX = 2,
};

-enum vhost_net_poll_state {
- VHOST_NET_POLL_DISABLED = 0,
- VHOST_NET_POLL_STARTED = 1,
- VHOST_NET_POLL_STOPPED = 2,
-};
-
struct vhost_net {
struct vhost_dev dev;
struct vhost_virtqueue vqs[VHOST_NET_VQ_MAX];
struct vhost_poll poll[VHOST_NET_VQ_MAX];
- /* Tells us whether we are polling a socket for TX.
- * We only do this when socket buffer fills up.
- * Protected by tx vq lock. */
- enum vhost_net_poll_state tx_poll_state;
/* Number of TX recently submitted.
* Protected by tx vq lock. */
unsigned tx_packets;
@@ -155,24 +145,6 @@ static void copy_iovec_hdr(const struct iovec *from, struct iovec *to,
}
}

-/* Caller must have TX VQ lock */
-static void tx_poll_stop(struct vhost_net *net)
-{
- if (likely(net->tx_poll_state != VHOST_NET_POLL_STARTED))
- return;
- vhost_poll_stop(net->poll + VHOST_NET_VQ_TX);
- net->tx_poll_state = VHOST_NET_POLL_STOPPED;
-}
-
-/* Caller must have TX VQ lock */
-static void tx_poll_start(struct vhost_net *net, struct socket *sock)
-{
- if (unlikely(net->tx_poll_state != VHOST_NET_POLL_STOPPED))
- return;
- vhost_poll_start(net->poll + VHOST_NET_VQ_TX, sock->file);
- net->tx_poll_state = VHOST_NET_POLL_STARTED;
-}
-
/* In case of DMA done not in order in lower device driver for some reason.
* upend_idx is used to track end of used idx, done_idx is used to track head
* of used idx. Once lower device DMA done contiguously, we will signal KVM
@@ -227,6 +199,7 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success)
static void handle_tx(struct vhost_net *net)
{
struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX];
+ struct vhost_poll *poll = net->poll + VHOST_NET_VQ_TX;
unsigned out, in, s;
int head;
struct msghdr msg = {
@@ -252,7 +225,8 @@ static void handle_tx(struct vhost_net *net)
wmem = atomic_read(&sock->sk->sk_wmem_alloc);
if (wmem >= sock->sk->sk_sndbuf) {
mutex_lock(&vq->mutex);
- tx_poll_start(net, sock);
+ if (vhost_poll_start(poll, sock->file))
+ vq_err(vq, "Fail to start TX polling\n");
mutex_unlock(&vq->mutex);
return;
}
@@ -261,7 +235,7 @@ static void handle_tx(struct vhost_net *net)
vhost_disable_notify(&net->dev, vq);

if (wmem < sock->sk->sk_sndbuf / 2)
- tx_poll_stop(net);
+ vhost_poll_stop(poll);
hdr_size = vq->vhost_hlen;
zcopy = vq->ubufs;

@@ -283,8 +257,10 @@ static void handle_tx(struct vhost_net *net)

wmem = atomic_read(&sock->sk->sk_wmem_alloc);
if (wmem >= sock->sk->sk_sndbuf * 3 / 4) {
- tx_poll_start(net, sock);
- set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
+ if (vhost_poll_start(poll, sock->file))
+ vq_err(vq, "Fail to start TX polling\n");
+ else
+ set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
break;
}
/* If more outstanding DMAs, queue the work.
@@ -294,8 +270,10 @@ static void handle_tx(struct vhost_net *net)
(vq->upend_idx - vq->done_idx) :
(vq->upend_idx + UIO_MAXIOV - vq->done_idx);
if (unlikely(num_pends > VHOST_MAX_PEND)) {
- tx_poll_start(net, sock);
- set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
+ if (vhost_poll_start(poll, sock->file))
+ vq_err(vq, "Fail to start TX polling\n");
+ else
+ set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
break;
}
if (unlikely(vhost_enable_notify(&net->dev, vq))) {
@@ -360,7 +338,8 @@ static void handle_tx(struct vhost_net *net)
}
vhost_discard_vq_desc(vq, 1);
if (err == -EAGAIN || err == -ENOBUFS)
- tx_poll_start(net, sock);
+ if (vhost_poll_start(poll, sock->file))
+ vq_err(vq, "Fail to start TX polling\n");
break;
}
if (err != len)
@@ -623,7 +602,6 @@ static int vhost_net_open(struct inode *inode, struct file *f)

vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT, dev);
vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN, dev);
- n->tx_poll_state = VHOST_NET_POLL_DISABLED;

f->private_data = n;

@@ -633,29 +611,25 @@ static int vhost_net_open(struct inode *inode, struct file *f)
static void vhost_net_disable_vq(struct vhost_net *n,
struct vhost_virtqueue *vq)
{
+ struct vhost_poll *poll = n->poll + (vq - n->vqs);
+
if (!vq->private_data)
return;
- if (vq == n->vqs + VHOST_NET_VQ_TX) {
- tx_poll_stop(n);
- n->tx_poll_state = VHOST_NET_POLL_DISABLED;
- } else
- vhost_poll_stop(n->poll + VHOST_NET_VQ_RX);
+ vhost_poll_stop(poll);
}

-static void vhost_net_enable_vq(struct vhost_net *n,
+static int vhost_net_enable_vq(struct vhost_net *n,
struct vhost_virtqueue *vq)
{
struct socket *sock;
+ struct vhost_poll *poll = n->poll + (vq - n->vqs);

sock = rcu_dereference_protected(vq->private_data,
lockdep_is_held(&vq->mutex));
if (!sock)
- return;
- if (vq == n->vqs + VHOST_NET_VQ_TX) {
- n->tx_poll_state = VHOST_NET_POLL_STOPPED;
- tx_poll_start(n, sock);
- } else
- vhost_poll_start(n->poll + VHOST_NET_VQ_RX, sock->file);
+ return 0;
+
+ return vhost_poll_start(poll, sock->file);
}

static struct socket *vhost_net_stop_vq(struct vhost_net *n,
@@ -833,7 +807,9 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
r = vhost_init_used(vq);
if (r)
goto err_used;
- vhost_net_enable_vq(n, vq);
+ r = vhost_net_enable_vq(n, vq);
+ if (r)
+ goto err_used;

oldubufs = vq->ubufs;
vq->ubufs = ubufs;
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 34389f7..5c7a466 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -77,26 +77,41 @@ void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
init_poll_funcptr(&poll->table, vhost_poll_func);
poll->mask = mask;
poll->dev = dev;
+ poll->wqh = NULL;

vhost_work_init(&poll->work, fn);
}

+/* Stop polling a file. After this function returns, it becomes safe to drop the
+ * file reference. You must also flush afterwards. */
+void vhost_poll_stop(struct vhost_poll *poll)
+{
+ if (poll->wqh) {
+ remove_wait_queue(poll->wqh, &poll->wait);
+ poll->wqh = NULL;
+ }
+}
+
/* Start polling a file. We add ourselves to file's wait queue. The caller must
* keep a reference to a file until after vhost_poll_stop is called. */
-void vhost_poll_start(struct vhost_poll *poll, struct file *file)
+int vhost_poll_start(struct vhost_poll *poll, struct file *file)
{
unsigned long mask;
+ int ret = 0;
+
+ if (poll->wqh)
+ return -EBUSY;

mask = file->f_op->poll(file, &poll->table);
if (mask)
vhost_poll_wakeup(&poll->wait, 0, 0, (void *)mask);
-}

-/* Stop polling a file. After this function returns, it becomes safe to drop the
- * file reference. You must also flush afterwards. */
-void vhost_poll_stop(struct vhost_poll *poll)
-{
- remove_wait_queue(poll->wqh, &poll->wait);
+ if (mask & POLLERR) {
+ ret = -EINVAL;
+ vhost_poll_stop(poll);
+ }
+
+ return ret;
}

static bool vhost_work_seq_done(struct vhost_dev *dev, struct vhost_work *work,
@@ -792,7 +807,7 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp)
fput(filep);

if (pollstart && vq->handle_kick)
- vhost_poll_start(&vq->poll, vq->kick);
+ r = vhost_poll_start(&vq->poll, vq->kick);

mutex_unlock(&vq->mutex);

diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 2639c58..17261e2 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -42,7 +42,7 @@ void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work);

void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
unsigned long mask, struct vhost_dev *dev);
-void vhost_poll_start(struct vhost_poll *poll, struct file *file);
+int vhost_poll_start(struct vhost_poll *poll, struct file *file);
void vhost_poll_stop(struct vhost_poll *poll);
void vhost_poll_flush(struct vhost_poll *poll);
void vhost_poll_queue(struct vhost_poll *poll);
--
1.7.1