linux-kernel - Re: [PATCH 1/1] dax: initialize variable pfn before using it

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Date:   Tue, 5 Sep 2017 12:37:30 -0600
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     Nicolas Iooss <nicolas.iooss_linux@....org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Matthew Wilcox <mawilcox@...rosoft.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] dax: initialize variable pfn before using it

On Sun, Sep 03, 2017 at 10:30:00AM +0200, Nicolas Iooss wrote:
> Function dax_pmd_insert_mapping() contains the following code:
> 
>         pfn_t pfn;
>         if (bdev_dax_pgoff(bdev, sector, size, &pgoff) != 0)
>             goto fallback;
>         /* ... */
>     fallback:
>       trace_dax_pmd_insert_mapping_fallback(inode, vmf, length, pfn, ret);
> 
> When the condition in the if statement fails, the function calls
> trace_dax_pmd_insert_mapping_fallback() with an uninitialized pfn value.
> 
> This issue has been found while building the kernel with clang. The
> compiler reported:
> 
>     fs/dax.c:1280:6: error: variable 'pfn' is used uninitialized
>     whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>         if (bdev_dax_pgoff(bdev, sector, size, &pgoff) != 0)
>             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     fs/dax.c:1310:60: note: uninitialized use occurs here
>       trace_dax_pmd_insert_mapping_fallback(inode, vmf, length, pfn, ret);
>                                                                      ^~~
> 
> Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@....org>

Yep this looks good.  Thanks for the fix.

Reviewed-by: Ross Zwisler <ross.zwisler@...ux.intel.com>

> ---
>  fs/dax.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index ab925dc6647a..20e6d76d6fff 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1283,7 +1283,7 @@ static int dax_pmd_insert_mapping(struct vm_fault *vmf, struct iomap *iomap,
>  	void *ret = NULL, *kaddr;
>  	long length = 0;
>  	pgoff_t pgoff;
> -	pfn_t pfn;
> +	pfn_t pfn = {};
>  	int id;
>  
>  	if (bdev_dax_pgoff(bdev, sector, size, &pgoff) != 0)
> -- 
> 2.14.1
>