Re: [PATCH v3 2/2] virtio_ring: check desc == NULL when packed and indirect

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Oct 19, 2021 at 07:12:26PM +0800, Xuan Zhuo wrote:
> On Tue, 19 Oct 2021 07:07:58 -0400, Michael S. Tsirkin <mst@redhat.com> wrote:
> > On Tue, Oct 19, 2021 at 06:56:57PM +0800, Xuan Zhuo wrote:
> > > In the case of packed, use indirect desc, since desc is allocated by
> > > kmalloc_array(), we should check whether its return value is NULL.
> > >
> > > This patch alloc desc inside virtqueue_add_packe(), if desc == NULL,
> >
> > Can we manage without typos in commit log please?
> 
> I'm sorry. virtqueue_add_packe => virtqueue_add_packed
> 
> >
> > > fall back to not using indirect.
> >
> >
> > It should say why is the patch created, and how it's fixed,
> > as opposed to repating what patch does.
> >
> > E.g.
> >
> > when using indirect with packed, we don't check for
> > allocation failures. Check and fall back on direct.
> 
> 
> It's better.  I know how to do it.
> 
> 
> >
> >
> >
> > > Fixes: 1ce9e6055fa ("virtio_ring: introduce packed ring support")
> > > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > > Acked-by: Jason Wang <jasowang@redhat.com>
> > > ---
> > >  drivers/virtio/virtio_ring.c | 14 +++++++++-----
> > >  1 file changed, 9 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > index 91a46c4da87d..62323c27bfe4 100644
> > > --- a/drivers/virtio/virtio_ring.c
> > > +++ b/drivers/virtio/virtio_ring.c
> > > @@ -1051,20 +1051,19 @@ 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[],
> > > +					 struct vring_packed_desc *desc,
> > >  					 unsigned int total_sg,
> > >  					 unsigned int out_sgs,
> > >  					 unsigned int in_sgs,
> > >  					 void *data,
> > >  					 gfp_t gfp)
> >
> > So this gets desc and will free it. I don't much like this.
> 
> Under normal circumstances, this function will not release desc. It will
> actually release "desc" in detach_buf_packed(). Of course, if you encounter
> an error in this function, it will also release desc in this function.
> 
> If we call alloc_indirect_packed() in virtqueue_add_indirect_packed() it is also
> possible, we need to make virtqueue_add_indirect_packed() return a special
> return value.
> 
> Thanks.


that seems cleaner

> >
> >
> > >  {
> > > -	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 +1190,14 @@ 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);
> > > +	}
> > >
> > >  	head = vq->packed.next_avail_idx;
> > >  	avail_used_flags = vq->packed.avail_used_flags;
> > > --
> > > 2.31.0
> >

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