Re: [PATCH 8/9] xfs: record inode buf errors as a xref error in inode scrubber

[Brian Foster <bfoster@redhat.com>]

On Wed, Mar 21, 2018 at 01:50:08PM -0700, Darrick J. Wong wrote:
> On Wed, Mar 21, 2018 at 01:42:49PM -0400, Brian Foster wrote:
> > On Wed, Mar 14, 2018 at 05:30:20PM -0700, Darrick J. Wong wrote:
> > > From: Darrick J. Wong <darrick.wong@oracle.com>
> > > 
> > > During the inode btree scrubs we try to confirm the freemask bits
> > > against the inode records.  If the inode buffer read fails, this is a
> > > cross-referencing error, not a corruption of the inode btree itself.
> > > Use the xref_process_error call here.  Found via core.version middlebit
> > > fuzz in xfs/415.
> > > 
> > 
> > What's the difference/consequence of this change?
> 
> For now, more accurate reporting of the outcome of scrubbing the inobt.
> If xfs_imap_to_bp returns EFSCORRUPTED that means that it found the
> inode buffer, loaded it, and the verifier for the inode records failed.
> Therefore, we need to communicate to userspace that the inobt looks ok
> but we were unable to confirm that something the inobt points to (the
> inode chunk) agrees with the the pointer.  That's an xref error, not a
> corruption error.
> 
> Once we start on the xfs_scrub repair support, you'll see in the patches
> that prior to scanning the inodes in the filesystem, we need to know
> whether or not the agi and the inobt are ok.  If the agi or inobt scan
> shows corruption, we need to rebuild them (or abort).  If however, the
> scan only says cross-referencing error, then we conclude that the inobt
> is ok but the inodes are not, and proceed with the inode scan to find
> the bad inode and repair it.
> 

Ok, so it's a reporting/conceptual thing. Seems fine, it's just hard to
confirm that from deep in the scrub code unless the commit log explains
why the change is made (which looks like v2 does...).

Brian

> --D
> 
> > Brian
> > 
> > > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > > ---
> > >  fs/xfs/scrub/ialloc.c |    3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > 
> > > diff --git a/fs/xfs/scrub/ialloc.c b/fs/xfs/scrub/ialloc.c
> > > index 63ab3f9..32e0d1a 100644
> > > --- a/fs/xfs/scrub/ialloc.c
> > > +++ b/fs/xfs/scrub/ialloc.c
> > > @@ -259,7 +259,8 @@ xfs_scrub_iallocbt_check_freemask(
> > >  
> > >  		error = xfs_imap_to_bp(mp, bs->cur->bc_tp, &imap,
> > >  				&dip, &bp, 0, 0);
> > > -		if (!xfs_scrub_btree_process_error(bs->sc, bs->cur, 0, &error))
> > > +		if (!xfs_scrub_btree_xref_process_error(bs->sc, bs->cur, 0,
> > > +				&error))
> > >  			continue;
> > >  
> > >  		/* Which inodes are free? */
> > > 
> > > --
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