From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [PATCH 1/6] xen-gntdev: Fix circular locking
	dependency
Date: Tue, 14 Dec 2010 13:11:18 -0800
Message-ID: <4D07DD76.2010900@goop.org>
References: <1292338553-20575-1-git-send-email-dgdegra@tycho.nsa.gov>
	<1292338553-20575-2-git-send-email-dgdegra@tycho.nsa.gov>
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To: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Cc: xen-devel@lists.xensource.com, Ian.Campbell@citrix.com
List-Id: xen-devel@lists.xenproject.org

On 12/14/2010 06:55 AM, Daniel De Graaf wrote:
> apply_to_page_range will acquire PTE lock while priv->lock is held, and
> mn_invl_range_start tries to acquire priv->lock with PTE already held.
> Fix by not holding priv->lock during the entire map operation.

Is priv->lock needed to protect the contents of map?

    J

> Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
> ---
>  drivers/xen/gntdev.c |   19 +++++++++----------
>  1 files changed, 9 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index a33e443..c582804 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -581,23 +581,22 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>  	if (!(vma->vm_flags & VM_WRITE))
>  		map->flags |= GNTMAP_readonly;
>  
> +	spin_unlock(&priv->lock);
> +
>  	err = apply_to_page_range(vma->vm_mm, vma->vm_start,
>  				  vma->vm_end - vma->vm_start,
>  				  find_grant_ptes, map);
> -	if (err) {
> -		goto unlock_out;
> -		if (debug)
> -			printk("%s: find_grant_ptes() failure.\n", __FUNCTION__);
> -	}
> +	if (err)
> +		return err;
>  
>  	err = map_grant_pages(map);
> -	if (err) {
> -		goto unlock_out;
> -		if (debug)
> -			printk("%s: map_grant_pages() failure.\n", __FUNCTION__);
> -	}
> +	if (err)
> +		return err;
> +
>  	map->is_mapped = 1;
>  
> +	return 0;
> +
>  unlock_out:
>  	spin_unlock(&priv->lock);
>  	return err;