Re: [Xen-devel] [PATCH] xen/gntdev: Don't allocate struct gntdev_copy_batch on stack

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 15/01/16 19:43, Boris Ostrovsky wrote:
> struct gntdev_copy_batch is over 1300 bytes in size, we shouldn't
> put it on stack.
>
> Some compilers (e.g. 5.2.1) complain:
>  drivers/xen/gntdev.c: In function âgntdev_ioctl_grant_copy.isra.5â:
>  drivers/xen/gntdev.c:949:1: warning: the frame size of 1416 bytes
>   is larger than 1024 bytes [-Wframe-larger-than=]
>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> ---
>  drivers/xen/gntdev.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index dc49538..43a2c1c 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -915,15 +915,19 @@ static int gntdev_grant_copy_seg(struct 
> gntdev_copy_batch *batch,
>  static long gntdev_ioctl_grant_copy(struct gntdev_priv *priv, void __user *u)
>  {
>       struct ioctl_gntdev_grant_copy copy;
> -     struct gntdev_copy_batch batch;
> +     struct gntdev_copy_batch *batch;
>       unsigned int i;
>       int ret = 0;
>  
>       if (copy_from_user(&copy, u, sizeof(copy)))
>               return -EFAULT;
>  
> -     batch.nr_ops = 0;
> -     batch.nr_pages = 0;
> +     batch = kmalloc(sizeof(*batch), GFP_KERNEL);
> +     if (!batch)
> +             return -ENOMEM;
> +
> +     batch->nr_ops = 0;
> +     batch->nr_pages = 0;
>  
>       for (i = 0; i < copy.count; i++) {
>               struct gntdev_grant_copy_segment seg;
> @@ -933,18 +937,20 @@ static long gntdev_ioctl_grant_copy(struct gntdev_priv 
> *priv, void __user *u)
>                       goto out;
>               }
>  
> -             ret = gntdev_grant_copy_seg(&batch, &seg, 
> &copy.segments[i].status);
> +             ret = gntdev_grant_copy_seg(batch, &seg,
> +                     &copy.segments[i].status);
>               if (ret < 0)
>                       goto out;
>  
>               cond_resched();
>       }
> -     if (batch.nr_ops)
> -             ret = gntdev_copy(&batch);
> +     if (batch->nr_ops)
> +             ret = gntdev_copy(batch);

You presumably want a kfree() here?

>       return ret;
>  
>    out:
> -     gntdev_put_pages(&batch);
> +     gntdev_put_pages(batch);
> +     kfree(batch);
>       return ret;
>  }
>  


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