linux-kernel - Re: [Xen-devel] [PATCH] xen/gntdev: Don't allocate struct gntdev_copy

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Message-ID: <56994D79.1010702@citrix.com>
Date:	Fri, 15 Jan 2016 19:50:17 +0000
From:	Andrew Cooper <andrew.cooper3@...rix.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	<konrad.wilk@...cle.com>, <david.vrabel@...rix.com>
CC:	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] xen/gntdev: Don't allocate struct
 gntdev_copy_batch on stack

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 ‘gntdev_ioctl_grant_copy.isra.5’:
>  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@...cle.com>
> ---
>  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;
>  }
>