Hi,
On 25/09/2018 13:36, xiangxia.m.yue@xxxxxxxxx wrote:
> From: Tonghao Zhang <xiangxia.m.yue@xxxxxxxxx>
>
> This patch changes the way that lock all vqs
> at the same, to lock them one by one. It will
> be used for next patch to avoid the deadlock.
>
> Signed-off-by: Tonghao Zhang <xiangxia.m.yue@xxxxxxxxx>
> Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> ---
> drivers/vhost/vhost.c | 24 +++++++-----------------
> 1 file changed, 7 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index b13c6b4..f52008b 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -294,8 +294,11 @@ static void vhost_vq_meta_reset(struct vhost_dev *d)
> {
> int i;
>
> - for (i = 0; i < d->nvqs; ++i)
> + for (i = 0; i < d->nvqs; ++i) {
> + mutex_lock(&d->vqs[i]->mutex);
> __vhost_vq_meta_reset(d->vqs[i]);
> + mutex_unlock(&d->vqs[i]->mutex);
> + }
> }
>
> static void vhost_vq_reset(struct vhost_dev *dev,
> @@ -891,20 +894,6 @@ static inline void __user *__vhost_get_user(struct vhost_virtqueue *vq,
> #define vhost_get_used(vq, x, ptr) \
> vhost_get_user(vq, x, ptr, VHOST_ADDR_USED)
>
> -static void vhost_dev_lock_vqs(struct vhost_dev *d)
> -{
> - int i = 0;
> - for (i = 0; i < d->nvqs; ++i)
> - mutex_lock_nested(&d->vqs[i]->mutex, i);
> -}
> -
> -static void vhost_dev_unlock_vqs(struct vhost_dev *d)
> -{
> - int i = 0;
> - for (i = 0; i < d->nvqs; ++i)
> - mutex_unlock(&d->vqs[i]->mutex);
> -}
> -
> static int vhost_new_umem_range(struct vhost_umem *umem,
> u64 start, u64 size, u64 end,
> u64 userspace_addr, int perm)
> @@ -954,7 +943,10 @@ static void vhost_iotlb_notify_vq(struct vhost_dev *d,
> if (msg->iova <= vq_msg->iova &&
> msg->iova + msg->size - 1 >= vq_msg->iova &&
> vq_msg->type == VHOST_IOTLB_MISS) {
> + mutex_lock(&node->vq->mutex);
This seems to introduce a deadlock (and sleep-in-atomic): the vq->mutex
is taken while the IOTLB spinlock is held (taken earlier in
vhost_iotlb_notify_vq()). On the vhost_iotlb_miss() path, the IOTLB
spinlock is taken while the vq->mutex is held.
I'm not sure how to fix it. Given that we're holding dev->mutex, that
vq->poll only seems to be modified under dev->mutex, and assuming that
vhost_poll_queue(vq->poll) can be called concurrently, is it safe to
simply not take vq->mutex here?
Thanks,
Jean
> vhost_poll_queue(&node->vq->poll);
> + mutex_unlock(&node->vq->mutex);
> +
> list_del(&node->node);
> kfree(node);
> }
> @@ -986,7 +978,6 @@ static int vhost_process_iotlb_msg(struct vhost_dev *dev,
> int ret = 0;
>
> mutex_lock(&dev->mutex);
> - vhost_dev_lock_vqs(dev);
> switch (msg->type) {
> case VHOST_IOTLB_UPDATE:
> if (!dev->iotlb) {
> @@ -1020,7 +1011,6 @@ static int vhost_process_iotlb_msg(struct vhost_dev *dev,
> break;
> }
>
> - vhost_dev_unlock_vqs(dev);
> mutex_unlock(&dev->mutex);
>
> return ret;
>
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