From: Dan Carpenter <dan.carpenter@oracle.com>
To: Dave Chinner <david@fromorbit.com>, Christoph Hellwig <hch@lst.de>
Cc: djwong@kernel.org, linux-xfs@vger.kernel.org
Subject: Re: [bug report] xfs: pass the goal of the incore inode walk to xfs_inode_walk()
Date: Fri, 13 Aug 2021 10:38:12 +0300 [thread overview]
Message-ID: <20210813073812.GX22532@kadam> (raw)
In-Reply-To: <20210812214048.GE3657114@dread.disaster.area>
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...
You're analysis is correct, but I'm looking at a newer version of the
code and I blamed the wrong commit. It should be commit 777eb1fa857e
("xfs: remove xfs_dqrele_all_inodes")
https://lore.kernel.org/linux-xfs/20210809065938.1199181-3-hch@lst.de/
That commit removes the "XFS_ICWALK_DQRELE = -1," line which
changes the enum type from int to unsigned int.
So this suggests that we should just remove the check for negative
values.
regards,
dan carpenter
>
> > 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...
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@fromorbit.com
next prev parent reply other threads:[~2021-08-13 7:38 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-12 6:42 [bug report] xfs: pass the goal of the incore inode walk to xfs_inode_walk() Dan Carpenter
2021-08-12 21:40 ` Dave Chinner
2021-08-12 22:41 ` Darrick J. Wong
2021-08-12 23:57 ` Dave Chinner
2021-08-13 8:12 ` Dan Carpenter
2021-08-13 7:38 ` Dan Carpenter [this message]
2021-08-13 8:15 ` Christoph Hellwig
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