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Date:   Wed, 13 Sep 2023 09:36:56 -0300
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Cong Liu <liucong2@kylinos.cn>
Cc:     alex.williamson@redhat.com, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fix build error in function vfio_combine_iova_ranges
Message-ID: <ZQGs6F5y3YzlAJaL@ziepe.ca>
References: <20230911124431.5e09f53b.alex.williamson@redhat.com>
 <20230912010736.19481-1-liucong2@kylinos.cn>
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On Tue, Sep 12, 2023 at 09:07:36AM +0800, Cong Liu wrote:
> when compiling with smatch check, the following errors were encountered:
> 
> drivers/vfio/vfio_main.c:957 vfio_combine_iova_ranges() error: uninitialized symbol 'last'.
> drivers/vfio/vfio_main.c:978 vfio_combine_iova_ranges() error: potentially dereferencing uninitialized 'comb_end'.
> drivers/vfio/vfio_main.c:978 vfio_combine_iova_ranges() error: potentially dereferencing uninitialized 'comb_start'.
> 
> this patch fix these error.
> 
> Signed-off-by: Cong Liu <liucong2@kylinos.cn>
> ---
>  drivers/vfio/vfio_main.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index 40732e8ed4c6..68a0a5081161 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -938,12 +938,13 @@ static int vfio_ioctl_device_feature_migration(struct vfio_device *device,
>  void vfio_combine_iova_ranges(struct rb_root_cached *root, u32 cur_nodes,
>  			      u32 req_nodes)
>  {
> -	struct interval_tree_node *prev, *curr, *comb_start, *comb_end;
> +	struct interval_tree_node *prev, *curr;
> +	struct interval_tree_node *comb_start = NULL, *comb_end = NULL;
>  	unsigned long min_gap, curr_gap;
>  
>  	/* Special shortcut when a single range is required */
>  	if (req_nodes == 1) {
> -		unsigned long last;
> +		unsigned long last = 0;
>  
>  		comb_start = interval_tree_iter_first(root, 0, ULONG_MAX);
>  		curr = comb_start;

These are not possible unless the list is empty, and assigning
zero/null isn't an improvement for that case it will just crash

Jason