Re: XFS warning in 2.6.18-rc4

["Jesper Juhl" <jesper.juhl@gmail.com>]

On 10/08/06, Nathan Scott <nathans@sgi.com> wrote:
> On Wed, Aug 09, 2006 at 11:04:53PM +0300, Meelis Roos wrote:
> > fs/xfs/xfs_bmap.c: In function 'xfs_bmapi':
> > fs/xfs/xfs_bmap.c:2662: warning: 'rtx' is used uninitialized in this function
>
> You have a particularly dense compiler, unfortunately.  This code
> has always been this way, its just a false cc warning that can be
> safely ignored until you upgrade to a fixed compiler (unless I'm
> missing something - please enlighten me if so).  It does seem to
> be the case that there is no way 'rtx' will be used uninitialised
> when xfs_rtpick_extent() doesn't fail... no?
>
Ok, I may be reading something wrong here, but I think the warning is
actually not correct.

In fs/xfs/xfs_rtalloc.c::xfs_rtpick_extent() there is this code :

...
        if ((error = xfs_trans_iget(mp, tp, mp->m_sb.sb_rbmino, 0,
                                        XFS_ILOCK_EXCL, &ip)))
                return error;
...
before anything even touches 'pick' (which is the last argument of
type "xfs_rtblock_t  *" which is what "&rtx" is being passed to that
function as, from fs/xfs/xfs_bmap.c::xfs_bmap_rtalloc() at line 2659
before 'rtx' then used at line 2662.

Look at this block of code from fs/xfs/xfs_bmap.c::xfs_bmap_rtalloc()  :

...
 2658:       if (ap->eof && ap->off == 0) {
 2659:                error = xfs_rtpick_extent(mp, ap->tp, ralen, &rtx);
 2660:                if (error)
 2661:                        return error;
 2662:                ap->rval = rtx * mp->m_sb.sb_rextsize;
 2663:        } else {
 2664:                ap->rval = 0;
 2665:        }
..

'rtx' has not been initialized in this function before this block of code.
If the call to xfs_rtpick_extent() should happen to fail from the
check quoted above, then 'rtx' will in fact be used uninitialized in
line 2662 - except that will never happen, because if the check in In
fs/xfs/xfs_rtalloc.c::xfs_rtpick_extent() fails then error will be !=
0 and then well never get down to line 2662.

Or am I missing something ?


PS. Above line numbers etc are from 2.6.18-rc4.


-- 
Jesper Juhl <jesper.juhl@gmail.com>
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