On Fri, Aug 13, 2021 at 07:40:48AM +1000, Dave Chinner wrote:
> On Thu, Aug 12, 2021 at 09:42:22AM +0300, Dan Carpenter wrote:
> > Hello Darrick J. Wong,
> >
> > The patch c809d7e948a1: "xfs: pass the goal of the incore inode walk
> > to xfs_inode_walk()" from Jun 1, 2021, leads to the following
> > Smatch static checker warning:
> >
> > fs/xfs/xfs_icache.c:52 xfs_icwalk_tag()
> > warn: unsigned 'goal' is never less than zero.
> >
> > fs/xfs/xfs_icache.c
> > 49 static inline unsigned int
> > 50 xfs_icwalk_tag(enum xfs_icwalk_goal goal)
> > 51 {
> > --> 52 return goal < 0 ? XFS_ICWALK_NULL_TAG : goal;
> >
> > This enum will be unsigned in GCC, so "goal" can't be negative.
>
> I think this is incorrect. The original C standard defines enums as
> signed integers, not unsigned. And according to the GCC manual
> (section 4.9 Structures, Unions, Enumerations, and Bit-Fields)
> indicates that C90 first defines the enum type to be compatible with
> the declared values. IOWs, for a build using C89 like the kernel
> does, enums should always be signed.
>
> This enum is defined as:
>
> enum xfs_icwalk_goal {
> /* Goals that are not related to tags; these must be < 0. */
> XFS_ICWALK_DQRELE = -1,
>
> /* Goals directly associated with tagged inodes. */
> XFS_ICWALK_BLOCKGC = XFS_ICI_BLOCKGC_TAG,
> XFS_ICWALK_RECLAIM = XFS_ICI_RECLAIM_TAG,
> };
>
> i.e. the enum is defined to clearly contain negative values and so
> GCC should be defining it as a signed integer regardless of the
> version of C being used...
>
> > Plus
> > we only pass 0-1 for goal (as far as Smatch can tell).
>
> Yup, smatch has definitely got that one wrong:
>
> xfs_dqrele_all_inodes()
> xfs_icwalk(mp, XFS_ICWALK_DQRELE, &icw);
> xfs_icwalk_get_perag(.... XFS_ICWALK_DQRELE)
> xfs_icwalk_tag(... XFS_ICWALK_DQRELE, ...)
>
> So this warning looks like an issue with smatch, not a bug in the
> code...
...unless Dan is running smatch against for-next, which removes
XFS_ICWALK_DQRELE and thus allows for an unsigned type to back the enum?
--D
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@xxxxxxxxxxxxx
