Re: [PATCH] virtio_ring: check desc == NULL when packed and indirect

On Mon, 27 Sep 2021 11:20:16 +0800, Jason Wang [off-list ref] wrote:

On Mon, Sep 27, 2021 at 11:06 AM Xuan Zhuo [off-list ref] wrote:

quoted

In the case of packed, use indirect desc, since desc is allocated by
kmalloc_array(), we should check whether its return value is NULL.

Fixes: 1ce9e6055fa ("virtio_ring: introduce packed ring support")
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
 drivers/virtio/virtio_ring.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index dd95dfd85e98..7dd381eae725 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c

@@ -1050,21 +1050,20 @@ static struct vring_packed_desc *alloc_indirect_packed(unsigned int total_sg,
 }

 static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
-                                      struct scatterlist *sgs[],
-                                      unsigned int total_sg,
-                                      unsigned int out_sgs,
-                                      unsigned int in_sgs,
-                                      void *data,
-                                      gfp_t gfp)
+                                        struct scatterlist *sgs[],
+                                        struct vring_packed_desc *desc,
+                                        unsigned int total_sg,
+                                        unsigned int out_sgs,
+                                        unsigned int in_sgs,
+                                        void *data,
+                                        gfp_t gfp)

It looks to me the style changes are mixed with bug fix here.

I will make a separate patch for the next version.

quoted

 {
-       struct vring_packed_desc *desc;
        struct scatterlist *sg;
        unsigned int i, n, err_idx;
        u16 head, id;
        dma_addr_t addr;

        head = vq->packed.next_avail_idx;
-       desc = alloc_indirect_packed(total_sg, gfp);

        if (unlikely(vq->vq.num_free < 1)) {
                pr_debug("Can't add buf len 1 - avail = 0\n");

@@ -1191,9 +1190,15 @@ 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)) {
+               desc = alloc_indirect_packed(total_sg, gfp);
+               if (desc) {
+                       return virtqueue_add_indirect_packed(vq, sgs, desc,
+                                                            total_sg,
+                                                            out_sgs, in_sgs,
+                                                            data, gfp);
+               }
+       }

Any reason that we can't fix virtqueue_add_indirect_packed()? It can
help to reduce the changeset and ease the backport.

The purpose of this is to fall back to not using indirect when
alloc_indirect_packed returns NULL.

If we check the return value of alloc_indirect_packed() in
virtqueue_add_indirect_packed(), then MUST check the error returned by
virtqueue_add_indirect_packed() to determine whether to fall back to the mode
that does not use indirect.

Thanks.

Thanks

quoted

        head = vq->packed.next_avail_idx;
        avail_used_flags = vq->packed.avail_used_flags;
--
2.31.0

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