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Message-ID: <20130116110015.GC13470@redhat.com>
Date: Wed, 16 Jan 2013 13:00:15 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH V5 2/3] vhost_net: handle polling errors when setting
backend
On Wed, Jan 16, 2013 at 06:34:00PM +0800, Jason Wang wrote:
> Currently, the polling errors were ignored, which can lead following issues:
>
> - vhost remove itself unconditionally from waitqueue when stopping the poll,
> this may crash the kernel since the previous attempt of starting may fail to
> add itself to the waitqueue
> - userspace may think the backend were successfully set even when the polling
> failed.
>
> Solve this by:
>
> - check poll->wqh before trying to remove from waitqueue
> - report polling errors in vhost_poll_start(), tx_poll_start(), the return value
> will be checked and returned when userspace want to set the backend
>
> After this fix, there still could be a polling failure after backend is set, it
> will addressed by the next patch.
>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
Looks ok but needs to be considered together with the next one,
to make sure we cover all cases.
> ---
> drivers/vhost/net.c | 27 ++++++++++++++++++---------
> drivers/vhost/vhost.c | 18 +++++++++++++++---
> drivers/vhost/vhost.h | 2 +-
> 3 files changed, 34 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index d10ad6f..959b1cd 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -165,12 +165,16 @@ static void tx_poll_stop(struct vhost_net *net)
> }
>
> /* Caller must have TX VQ lock */
> -static void tx_poll_start(struct vhost_net *net, struct socket *sock)
> +static int tx_poll_start(struct vhost_net *net, struct socket *sock)
> {
> + int ret;
> +
> 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;
> + return 0;
> + ret = vhost_poll_start(net->poll + VHOST_NET_VQ_TX, sock->file);
> + if (!ret)
> + net->tx_poll_state = VHOST_NET_POLL_STARTED;
> + return ret;
> }
>
> /* In case of DMA done not in order in lower device driver for some reason.
> @@ -642,20 +646,23 @@ static void vhost_net_disable_vq(struct vhost_net *n,
> vhost_poll_stop(n->poll + VHOST_NET_VQ_RX);
> }
>
> -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;
> + int ret;
>
> sock = rcu_dereference_protected(vq->private_data,
> lockdep_is_held(&vq->mutex));
> if (!sock)
> - return;
> + return 0;
> if (vq == n->vqs + VHOST_NET_VQ_TX) {
> n->tx_poll_state = VHOST_NET_POLL_STOPPED;
> - tx_poll_start(n, sock);
> + ret = tx_poll_start(n, sock);
> } else
> - vhost_poll_start(n->poll + VHOST_NET_VQ_RX, sock->file);
> + ret = vhost_poll_start(n->poll + VHOST_NET_VQ_RX, sock->file);
> +
> + return ret;
> }
>
> static struct socket *vhost_net_stop_vq(struct vhost_net *n,
> @@ -833,7 +840,9 @@ 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..9759249 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -77,26 +77,38 @@ 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);
> }
>
> /* 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;
>
> mask = file->f_op->poll(file, &poll->table);
> if (mask)
> vhost_poll_wakeup(&poll->wait, 0, 0, (void *)mask);
> + if (mask & POLLERR) {
> + if (poll->wqh)
> + remove_wait_queue(poll->wqh, &poll->wait);
> + ret = -EINVAL;
> + }
> +
> + return ret;
> }
>
> /* 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 (poll->wqh) {
> + remove_wait_queue(poll->wqh, &poll->wait);
> + poll->wqh = NULL;
> + }
> }
>
> static bool vhost_work_seq_done(struct vhost_dev *dev, struct vhost_work *work,
> @@ -792,7 +804,7 @@ 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
--
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