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

["Darrick J. Wong" <djwong@kernel.org>]

On Thu, Jan 28, 2021 at 10:34:12AM -0500, Brian Foster wrote:
> 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?

It only returns nonzero if isrt (the fifth parameter) is nonzero, and
only if the requested range is still not aligned to the rt extent size
after aligning it and eliminating any overlaps with existing extents.

--D

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