Re: [patch] xfs: bug widening binary "not" operation

Dave Chinner
2013-05-17T10:19:08Z

On Fri, May 17, 2013 at 09:31:59AM +0300, Dan Carpenter wrote:
> On Fri, May 17, 2013 at 09:03:14AM +1000, Dave Chinner wrote:
> > As it is, the static checker missed the:
> >
> > rounding = max_t(uint, ....);
> >
> > The line before the above usage. I posted a patch to fix this this
> > 2 weeks ago here:
> >
> > http://oss.sgi.com/pipermail/xfs/2013-May/025986.html
> >
>
> Ah. Grand. There is still a problem with the max_t(). The shift
> operation will wrap before we do the cast. It should be:

It probably looks that way, but it can't overflow as
mp->m_sb.sb_blocklog has a maximum value of 16 (i.e. 64k maximum
filesystem block size).

>
> - rounding = max_t(xfs_off_t, 1 << mp->m_sb.sb_blocklog, PAGE_CACHE_SIZE);
> + rounding = max_t(xfs_off_t, 1ULL << mp->m_sb.sb_blocklog, PAGE_CACHE_SIZE);

So it is safe the way it is and this is not necessary.

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com