Re: [PATCH 05/30] xfs: create inode pointer verifiers

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, Oct 13, 2017 at 04:22:20PM +1100, Dave Chinner wrote:
> On Thu, Oct 12, 2017 at 01:23:03PM -0700, Darrick J. Wong wrote:
> > On Wed, Oct 11, 2017 at 06:41:15PM -0700, Darrick J. Wong wrote:
> > > From: Darrick J. Wong <darrick.wong@oracle.com>
> > > 
> > > Create some helper functions to check that inode pointers point to
> > > somewhere within the filesystem and not at the static AG metadata.
> > > Move xfs_internal_inum and create a directory inode check function.
> > > We will use these functions in scrub and elsewhere.
> ....
> > > diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c
> > > index 988bb3f..da3652b 100644
> > > --- a/fs/xfs/libxfs/xfs_ialloc.c
> > > +++ b/fs/xfs/libxfs/xfs_ialloc.c
> > > @@ -2664,3 +2664,84 @@ xfs_ialloc_pagi_init(
> > >  		xfs_trans_brelse(tp, bp);
> > >  	return 0;
> > >  }
> > > +
> > > +/* Calculate the first and last possible inode number in an AG. */
> > > +void
> > > +xfs_ialloc_aginode_range(
> 
> agino_range?
> 
> > > +	struct xfs_mount	*mp,
> > > +	xfs_agnumber_t		agno,
> > > +	xfs_agino_t		*first,
> > > +	xfs_agino_t		*last)
> > > +{
> > > +	xfs_agblock_t		eoag;
> > > +
> > > +	eoag = xfs_ag_block_count(mp, agno);
> > > +	*first = round_up(XFS_OFFBNO_TO_AGINO(mp, XFS_AGFL_BLOCK(mp) + 1, 0),
> > > +			XFS_INODES_PER_CHUNK);
> > > +	*last = round_down(XFS_OFFBNO_TO_AGINO(mp, eoag, 0),
> > > +			XFS_INODES_PER_CHUNK) - 1;
> > 
> > This is incorrect; we allocate inode chunks aligned to
> > xfs_ialloc_cluster_alignment blocks, which doesn't necessarily result in
> > ir_startino being aligned to XFS_INODES_PER_CHUNK.
> 
> *nod*
> 
> > I think the correct code is this:
> > 
> > 	/* Calculate the first inode. */
> > 	bno = round_up(XFS_AGFL_BLOCK(mp) + 1,
> > 			xfs_ialloc_cluster_alignment(mp));
> > 	*first = XFS_OFFBNO_TO_AGINO(mp, bno, 0);
> 
> *nod*
> 
> > 	/* Calculate the last inode. */
> > 	bno = round_down(eoag, xfs_ialloc_cluster_alignment(mp));
> > 	*last = XFS_OFFBNO_TO_AGINO(mp, bno, 0) - 1;
> 
> Bit tricky - I'm not sure that this will give the same inode number
> in all cases as rounding down to last valid chunk start offset and
> then adding (MAX(XFS_INODES_PER_CHUNK, inodes-per-block) - 1) to
> it....
> 
> > ...which unfortunately I didn't realize until trying to play with
> > nondefault geometry options (1k blocks, no sparse inodes).
> 
> Ok, that might explain a bunch of inode noise on my 1k block size
> test runs...
> 
> > > +/*
> > > + * Verify that an AG inode number pointer neither points outside the AG
> > > + * nor points at static metadata.
> > > + */
> > > +bool
> > > +xfs_verify_agino_ptr(
> 
> Again, I'd probably drop the _ptr suffix here.
> 
> > > +	struct xfs_mount	*mp,
> > > +	xfs_agnumber_t		agno,
> > > +	xfs_agino_t		agino)
> > > +{
> > > +	xfs_agino_t		first;
> > > +	xfs_agino_t		last;
> > > +	int			ioff;
> > > +
> > > +	ioff = XFS_AGINO_TO_OFFSET(mp, agino);
> > > +	xfs_ialloc_aginode_range(mp, agno, &first, &last);
> > > +	return agino >= first && agino <= last &&
> > > +	       ioff < (1 << mp->m_sb.sb_inopblog);
> 
> This ioff check will always evaluate as true, yes?
> 
> ioff	= XFS_AGINO_TO_OFFSET(i)
> 	= ((i) & XFS_INO_MASK(XFS_INO_OFFSET_BITS(mp)))
> 	= (i & XFS_INO_MASK((mp)->m_sb.sb_inopblog))
> 	= (i & (uint32_t)((1ULL << (mp)->m_sb.sb_inopblog)) - 1)
> 
> say sb_inopblog = 8:
> 
> ioff	= (i & 0xFF)
> 
> And so:
> 
> 	ioff < (1 << 8)
> 
> will always be true.
> 
> So I'm not sure this check is needed?

Indeed not.

--D

> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com
> --
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