Re: [PATCH] xfs: Fix 'set but not used' warning in xfs_bmap_compute_alignments()

[Brian Foster <bfoster@redhat.com>]

On Wed, Jan 27, 2021 at 02:35:37PM +0530, Chandan Babu R wrote:
> With both CONFIG_XFS_DEBUG and CONFIG_XFS_WARN disabled, the only reference to
> local variable "error" in xfs_bmap_compute_alignments() gets eliminated during
> pre-processing stage of the compilation process. This causes the compiler to
> generate a "set but not used" warning.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
> ---
> This patch is applicable on top of current xfs-linux/for-next branch.
> 
>  fs/xfs/libxfs/xfs_bmap.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 2cd24bb06040..ba56554e8c05 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -3471,7 +3471,6 @@ xfs_bmap_compute_alignments(
>  	struct xfs_mount	*mp = args->mp;
>  	xfs_extlen_t		align = 0; /* minimum allocation alignment */
>  	int			stripe_align = 0;
> -	int			error;
>  
>  	/* stripe alignment for allocation is determined by mount parameters */
>  	if (mp->m_swidth && (mp->m_flags & XFS_MOUNT_SWALLOC))
> @@ -3484,10 +3483,10 @@ xfs_bmap_compute_alignments(
>  	else if (ap->datatype & XFS_ALLOC_USERDATA)
>  		align = xfs_get_extsz_hint(ap->ip);
>  	if (align) {
> -		error = xfs_bmap_extsize_align(mp, &ap->got, &ap->prev,
> -						align, 0, ap->eof, 0, ap->conv,
> -						&ap->offset, &ap->length);
> -		ASSERT(!error);
> +		if (xfs_bmap_extsize_align(mp, &ap->got, &ap->prev,
> +			align, 0, ap->eof, 0, ap->conv, &ap->offset,
> +			&ap->length))
> +			ASSERT(0);

I was wondering if we should just make xfs_bmap_extsize_align() return
void and push the asserts down into the function itself, but it looks
like xfs_bmap_rtalloc() actually handles the error. Any idea on why we
might have that inconsistency?

Brian

>  		ASSERT(ap->length);
>  	}
>  
> -- 
> 2.29.2
>