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SubjectRe: [PATCH 1/2] vhost_net: correct error hanlding in vhost_net_set_backend()
On 12/27/2012 09:03 PM, Michael S. Tsirkin wrote:
> On Thu, Dec 27, 2012 at 02:39:20PM +0800, Jason Wang wrote:
>> 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.
> Maybe it could but this patch just ignores these errors.
> And it's not clear how would userspace handle these errors.

Not all were ignored, one example is vhost_net_enable_vq(), this could
be used to let userspace know the fd were not setup correctly.
> Also, since we have a reference on the fd, it would seem
> that once poll succeeds it can't fail in the future.

Right.
>
> So two other options would make more sense to me:
> - if vhost is bound to tun without SETIFF, fail this immediately
> - if vhost is bound to tun without SETIFF, defer polling
> until SETIFF
>
> Option 1 would seem much easier to implement, I think it's
> preferable.

Option 1 seems better, since userspace may also disable a queue in the
meantime. Will add a vq_err() and break out of the loop when fails to
start the polling.
>> 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;
>> }
>>
> Hmm, interesting. I note that tun has this:
>
> if (tun->dev->reg_state != NETREG_REGISTERED)
> mask = POLLERR;
>
> So apparently we sometimes return POLLERR when poll
> did succeed, then test below wouldn't remove
> from wqh in this case. Maybe it's a bug in tun,
> need to look into this.

Looks a bug of tun to me, looks like a POLLHUP is better here.
>
>> /* 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. */
> tx vq lock does not make sense in this context.

Yes, thanks for pointing this out.
>> + 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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