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Subject[PATCH 2/2] vhost: handle polling failure
Date
Currently, polling error were ignored in vhost. This may lead some issues (e.g
kenrel crash when passing a tap fd to vhost before calling TUNSETIFF). Fix this
by:

- extend the idea of vhost_net_poll_state to all vhost_polls
- change the state only when polling is succeed
- make vhost_poll_start() report errors to the caller, which could be used
caller or userspace.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/vhost/net.c | 75 +++++++++++++++++--------------------------------
drivers/vhost/vhost.c | 16 +++++++++-
drivers/vhost/vhost.h | 11 ++++++-
3 files changed, 50 insertions(+), 52 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 629d6b5..56e7f5a 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
@@ -252,7 +224,7 @@ 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);
+ vhost_poll_start(net->poll + VHOST_NET_VQ_TX, sock->file);
mutex_unlock(&vq->mutex);
return;
}
@@ -261,7 +233,7 @@ 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(net->poll + VHOST_NET_VQ_TX);
hdr_size = vq->vhost_hlen;
zcopy = vq->ubufs;

@@ -283,7 +255,8 @@ 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);
+ vhost_poll_start(net->poll + VHOST_NET_VQ_TX,
+ sock->file);
set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
break;
}
@@ -294,7 +267,8 @@ 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);
+ vhost_poll_start(net->poll + VHOST_NET_VQ_TX,
+ sock->file);
set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
break;
}
@@ -360,7 +334,8 @@ static void handle_tx(struct vhost_net *net)
}
vhost_discard_vq_desc(vq, 1);
if (err == -EAGAIN || err == -ENOBUFS)
- tx_poll_start(net, sock);
+ vhost_poll_start(net->poll + VHOST_NET_VQ_TX,
+ sock->file);
break;
}
if (err != len)
@@ -623,7 +598,6 @@ 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;

@@ -635,27 +609,26 @@ static void vhost_net_disable_vq(struct vhost_net *n,
{
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
+ if (vq == n->vqs + VHOST_NET_VQ_TX)
+ vhost_poll_stop(n->poll + VHOST_NET_VQ_TX);
+ else
vhost_poll_stop(n->poll + VHOST_NET_VQ_RX);
}

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

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;
+
+ n->poll[index].state = VHOST_POLL_STOPPED;
+ err = vhost_poll_start(n->poll + index, sock->file);
+ return err;
}

static struct socket *vhost_net_stop_vq(struct vhost_net *n,
@@ -831,12 +804,16 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
vq->ubufs = ubufs;
vhost_net_disable_vq(n, vq);
rcu_assign_pointer(vq->private_data, sock);
- vhost_net_enable_vq(n, vq);
+ r = vhost_net_enable_vq(n, vq);
+ if (r) {
+ sock = NULL;
+ goto err_enable;
+ }

r = vhost_init_used(vq);
if (r) {
sock = NULL;
- goto err_used;
+ goto err_enable;
}

n->tx_packets = 0;
@@ -861,7 +838,7 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
mutex_unlock(&n->dev.mutex);
return 0;

-err_used:
+err_enable:
if (oldubufs)
vhost_ubuf_put_and_wait(oldubufs);
if (oldsock)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 34389f7..1cb2604 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -77,26 +77,36 @@ 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->state = VHOST_POLL_DISABLED;

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

/* 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;
+ if (unlikely(poll->state != VHOST_POLL_STOPPED))
+ return 0;

mask = file->f_op->poll(file, &poll->table);
+ if (mask & POLLERR)
+ return -EINVAL;
if (mask)
vhost_poll_wakeup(&poll->wait, 0, 0, (void *)mask);
+ poll->state = VHOST_POLL_STARTED;
+ return 0;
}

/* 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 (likely(poll->state != VHOST_POLL_STARTED))
+ return;
remove_wait_queue(poll->wqh, &poll->wait);
+ poll->state = VHOST_POLL_STOPPED;
}

static bool vhost_work_seq_done(struct vhost_dev *dev, struct vhost_work *work,
@@ -791,8 +801,10 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp)
if (filep)
fput(filep);

- if (pollstart && vq->handle_kick)
+ if (pollstart && vq->handle_kick) {
+ vq->poll.state = VHOST_POLL_STOPPED;
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..98861d9 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -26,6 +26,12 @@ struct vhost_work {
unsigned done_seq;
};

+enum vhost_poll_state {
+ VHOST_POLL_DISABLED = 0,
+ VHOST_POLL_STARTED = 1,
+ VHOST_POLL_STOPPED = 2,
+};
+
/* Poll a file (eventfd or socket) */
/* Note: there's nothing vhost specific about this structure. */
struct vhost_poll {
@@ -35,6 +41,9 @@ struct vhost_poll {
struct vhost_work work;
unsigned long mask;
struct vhost_dev *dev;
+ /* Tells us whether we are polling a file.
+ * Protected by tx vq lock. */
+ enum vhost_poll_state state;
};

void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn);
@@ -42,7 +51,7 @@ 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


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