Re: [PATCH 06/12] xfs: only written file data blocks can be shared

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Oct 14, 2026 at 10:25:53AM +0200, Carlos Maiolino wrote:
> On Mon, Oct 12, 2026 at 11:06:46PM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@kernel.org>
> > 
> > LOLLM noticed that xchk_refcountbt_rmap_check (and its rt equivalent)
> > will count any rmap owner towards the shared count.  However, the only
> > blocks that can be shared between xfs files are written file data
> > blocks; and the only blocks that can have single-refcount entries are
> > COW staging extents.  Fix the checking code.
> > 
> > Cc: <stable@vger.kernel.org> # v4.16
> > Fixes: dbde19da963706 ("xfs: cross-reference the rmapbt data with the refcountbt")
> > Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
> > Assisted-by: LOLLM # finding obvious bugs
> 
> This patch conflicts with Eric's:
> 
> 1d55a102780 xfs: re-use refcount scrub/repair code for rtrefcount
> 
> I'm just stripping off the rtrefcountbt part of this, the final result
> is here:
> 
> commit 634b63baf05062988456a0bd5df2696c14ea2949
> Author: Darrick J. Wong <djwong@kernel.org>
> Date:   Mon Oct 12 23:06:46 2026 -0700
> 
>     xfs: only written file data blocks can be shared

Yep, that looks good to me!

--D

> 
> 
> > ---
> >  fs/xfs/scrub/refcount.c   |   12 ++++++++++++
> >  fs/xfs/scrub/rtrefcount.c |   12 ++++++++++++
> >  2 files changed, 24 insertions(+)
> > 
> > 
> > diff --git a/fs/xfs/scrub/refcount.c b/fs/xfs/scrub/refcount.c
> > index f8c51d8fbb3da5..a900d13c9e27c0 100644
> > --- a/fs/xfs/scrub/refcount.c
> > +++ b/fs/xfs/scrub/refcount.c
> > @@ -129,6 +129,18 @@ xchk_refcountbt_rmap_check(
> >  		return 0;
> >  	}
> >  
> > +	/*
> > +	 * The refcount btree should only have records for written file data
> > +	 * blocks or for COW staging blocks.
> > +	 */
> > +	if ((XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) &&
> > +	     rec->rm_owner != XFS_RMAP_OWN_COW) ||
> > +	    (rec->rm_flags & (XFS_RMAP_ATTR_FORK | XFS_RMAP_BMBT_BLOCK |
> > +			      XFS_RMAP_UNWRITTEN))) {
> > +		xchk_btree_xref_set_corrupt(refchk->sc, cur, 0);
> > +		return 0;
> > +	}
> > +
> >  	if (rec->rm_startblock <= refchk->bno && rm_last >= rc_last) {
> >  		/*
> >  		 * The rmap overlaps the refcount record, so we can confirm
> > diff --git a/fs/xfs/scrub/rtrefcount.c b/fs/xfs/scrub/rtrefcount.c
> > index 3d916d71a135dc..00da8e98506d63 100644
> > --- a/fs/xfs/scrub/rtrefcount.c
> > +++ b/fs/xfs/scrub/rtrefcount.c
> > @@ -144,6 +144,18 @@ xchk_rtrefcountbt_rmap_check(
> >  		return 0;
> >  	}
> >  
> > +	/*
> > +	 * The refcount btree should only have records for written file data
> > +	 * blocks or for COW staging blocks.
> > +	 */
> > +	if ((XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) &&
> > +	     rec->rm_owner != XFS_RMAP_OWN_COW) ||
> > +	    (rec->rm_flags & (XFS_RMAP_ATTR_FORK | XFS_RMAP_BMBT_BLOCK |
> > +			      XFS_RMAP_UNWRITTEN))) {
> > +		xchk_btree_xref_set_corrupt(refchk->sc, cur, 0);
> > +		return 0;
> > +	}
> > +
> >  	if (rec->rm_startblock <= refchk->bno && rm_last >= rc_last) {
> >  		/*
> >  		 * The rmap overlaps the refcount record, so we can confirm
> > 
> > 
>