Linux Virtualization - Oct 2021 - [PATCH v4 2/2] virtio_ring: check desc == NULL when using indirect with packed

When using indirect with packed, we don't check for allocation failures.
This patch checks that and fall back on direct.

Fixes: 1ce9e6055fa ("virtio_ring: introduce packed ring support")
Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
---
 drivers/virtio/virtio_ring.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 91a46c4da87d..44a03b6e4dc4 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1065,6 +1065,9 @@ static int virtqueue_add_indirect_packed(struct
vring_virtqueue *vq,
 
 	head = vq->packed.next_avail_idx;
 	desc = alloc_indirect_packed(total_sg, gfp);
+	if (!desc)
+		/* fall back on direct */
+		return -EAGAIN;
 
 	if (unlikely(vq->vq.num_free < 1)) {
 		pr_debug("Can't add buf len 1 - avail = 0\n");
@@ -1176,6 +1179,7 @@ static inline int virtqueue_add_packed(struct virtqueue
*_vq,
 	unsigned int i, n, c, descs_used, err_idx;
 	__le16 head_flags, flags;
 	u16 head, id, prev, curr, avail_used_flags;
+	int err;
 
 	START_USE(vq);
 
@@ -1191,9 +1195,12 @@ static inline int virtqueue_add_packed(struct virtqueue
*_vq,
 
 	BUG_ON(total_sg == 0);
 
-	if (virtqueue_use_indirect(_vq, total_sg))
-		return virtqueue_add_indirect_packed(vq, sgs, total_sg,
-				out_sgs, in_sgs, data, gfp);
+	if (virtqueue_use_indirect(_vq, total_sg)) {
+		err = virtqueue_add_indirect_packed(vq, sgs, total_sg, out_sgs,
+						    in_sgs, data, gfp);
+		if (err != -EAGAIN)
+			return err;
+	}
 
 	head = vq->packed.next_avail_idx;
 	avail_used_flags = vq->packed.avail_used_flags;
-- 
2.31.0

On Tue, Oct 19, 2021 at 07:52:35PM +0800, Xuan Zhuo
wrote:
> When using indirect with packed, we don't check for allocation
failures.
> This patch checks that and fall back on direct.
> 
> Fixes: 1ce9e6055fa ("virtio_ring: introduce packed ring support")
> Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
> ---
>  drivers/virtio/virtio_ring.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 91a46c4da87d..44a03b6e4dc4 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -1065,6 +1065,9 @@ static int virtqueue_add_indirect_packed(struct
vring_virtqueue *vq,
>  
>  	head = vq->packed.next_avail_idx;
>  	desc = alloc_indirect_packed(total_sg, gfp);
> +	if (!desc)
> +		/* fall back on direct */
this comment belongs in virtqueue_add_packed right after
return.
> +		return -EAGAIN;
>  
-ENOMEM surely?
>  	if (unlikely(vq->vq.num_free < 1)) {
>  		pr_debug("Can't add buf len 1 - avail = 0\n");
> @@ -1176,6 +1179,7 @@ static inline int virtqueue_add_packed(struct
virtqueue *_vq,
>  	unsigned int i, n, c, descs_used, err_idx;
>  	__le16 head_flags, flags;
>  	u16 head, id, prev, curr, avail_used_flags;
> +	int err;
>  
>  	START_USE(vq);
>  
> @@ -1191,9 +1195,12 @@ static inline int virtqueue_add_packed(struct
virtqueue *_vq,
>  
>  	BUG_ON(total_sg == 0);
>  
> -	if (virtqueue_use_indirect(_vq, total_sg))
> -		return virtqueue_add_indirect_packed(vq, sgs, total_sg,
> -				out_sgs, in_sgs, data, gfp);
> +	if (virtqueue_use_indirect(_vq, total_sg)) {
> +		err = virtqueue_add_indirect_packed(vq, sgs, total_sg, out_sgs,
> +						    in_sgs, data, gfp);
> +		if (err != -EAGAIN)
> +			return err;
> +	}
>  
>  	head = vq->packed.next_avail_idx;
>  	avail_used_flags = vq->packed.avail_used_flags;
> -- 
> 2.31.0

On Tue, Oct 19, 2021 at 07:52:35PM +0800, Xuan Zhuo
wrote:
> When using indirect with packed, we don't check for allocation
failures.
> This patch checks that and fall back on direct.
> 
> Fixes: 1ce9e6055fa ("virtio_ring: introduce packed ring support")
> Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
Was a crash observed with this? It seems quite likely ...

> ---
>  drivers/virtio/virtio_ring.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 91a46c4da87d..44a03b6e4dc4 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -1065,6 +1065,9 @@ static int virtqueue_add_indirect_packed(struct
vring_virtqueue *vq,
>  
>  	head = vq->packed.next_avail_idx;
>  	desc = alloc_indirect_packed(total_sg, gfp);
> +	if (!desc)
> +		/* fall back on direct */
> +		return -EAGAIN;
>  
>  	if (unlikely(vq->vq.num_free < 1)) {
>  		pr_debug("Can't add buf len 1 - avail = 0\n");
> @@ -1176,6 +1179,7 @@ static inline int virtqueue_add_packed(struct
virtqueue *_vq,
>  	unsigned int i, n, c, descs_used, err_idx;
>  	__le16 head_flags, flags;
>  	u16 head, id, prev, curr, avail_used_flags;
> +	int err;
>  
>  	START_USE(vq);
>  
> @@ -1191,9 +1195,12 @@ static inline int virtqueue_add_packed(struct
virtqueue *_vq,
>  
>  	BUG_ON(total_sg == 0);
>  
> -	if (virtqueue_use_indirect(_vq, total_sg))
> -		return virtqueue_add_indirect_packed(vq, sgs, total_sg,
> -				out_sgs, in_sgs, data, gfp);
> +	if (virtqueue_use_indirect(_vq, total_sg)) {
> +		err = virtqueue_add_indirect_packed(vq, sgs, total_sg, out_sgs,
> +						    in_sgs, data, gfp);
> +		if (err != -EAGAIN)
> +			return err;
> +	}
>  
>  	head = vq->packed.next_avail_idx;
>  	avail_used_flags = vq->packed.avail_used_flags;
> -- 
> 2.31.0