Re: [PATCH 07/11] xfs: fully initialise temp leaf in xfs_attr3_leaf_compact

Ben Myers
2013-05-23T22:51:42Z

On Thu, May 23, 2013 at 09:58:20AM +1000, Dave Chinner wrote:
> On Wed, May 22, 2013 at 04:59:34PM -0500, Ben Myers wrote:
> > On Tue, May 21, 2013 at 06:02:06PM +1000, Dave Chinner wrote:
> > > From: Dave Chinner <dchinner@redhat.com>
> > >
> > > xfs_attr3_leaf_compact() uses a temporary buffer for compacting the
> > > the entries in a leaf. It copies the the original buffer into the
> > > temporary buffer, then zeros the original buffer completely. It then
> > > copies the entries back into the original buffer. However, the
> > > original buffer has not been correctly initialised, and so the
> > > movement of the entries goes horribly wrong.
> > >
> > > Make sure the zeroed destination buffer is fully initialised, and
> > > once we've set up the destination incore header appropriately, write
> > > is back to the buffer before starting to move entries around.
> > it
> >
> > >
> > > While debugging this, the _d/_s prefixes weren't sufficient to
> > > remind me what buffer was what, so rename then all _src/_dst.
> >
> > Yeah, it helps.
> >
> > > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > > ---
> > > fs/xfs/xfs_attr_leaf.c | 42 ++++++++++++++++++++++++++----------------
> > > 1 file changed, 26 insertions(+), 16 deletions(-)
> > >
> > > diff --git a/fs/xfs/xfs_attr_leaf.c b/fs/xfs/xfs_attr_leaf.c
> > > index 79ece72..5b03d15 100644
> > > --- a/fs/xfs/xfs_attr_leaf.c
> > > +++ b/fs/xfs/xfs_attr_leaf.c
> > > @@ -1445,11 +1445,12 @@ xfs_attr3_leaf_add_work(
> > > STATIC void
> > > xfs_attr3_leaf_compact(
> > > struct xfs_da_args *args,
> > > - struct xfs_attr3_icleaf_hdr *ichdr_d,
> > > + struct xfs_attr3_icleaf_hdr *ichdr_dst,
> > > struct xfs_buf *bp)
> > > {
> > > - xfs_attr_leafblock_t *leaf_s, *leaf_d;
> > > - struct xfs_attr3_icleaf_hdr ichdr_s;
> > > + struct xfs_attr_leafblock *leaf_src;
> > > + struct xfs_attr_leafblock *leaf_dst;
> > > + struct xfs_attr3_icleaf_hdr ichdr_src;
> > > struct xfs_trans *trans = args->trans;
> > > struct xfs_mount *mp = trans->t_mountp;
> > > char *tmpbuffer;
> > > @@ -1457,29 +1458,38 @@ xfs_attr3_leaf_compact(
> > > trace_xfs_attr_leaf_compact(args);
> > >
> > > tmpbuffer = kmem_alloc(XFS_LBSIZE(mp), KM_SLEEP);
> > > - ASSERT(tmpbuffer != NULL);
> > > memcpy(tmpbuffer, bp->b_addr, XFS_LBSIZE(mp));
> > > memset(bp->b_addr, 0, XFS_LBSIZE(mp));
> > > + leaf_src = (xfs_attr_leafblock_t *)tmpbuffer;
> > > + leaf_dst = bp->b_addr;
> > >
> > > /*
> > > - * Copy basic information
> > > + * Copy the on-disk header back into the destination buffer to ensure
> > > + * all the information in the header that is not part of the incore
> > > + * header structure is preserved.
> > > */
> > > - leaf_s = (xfs_attr_leafblock_t *)tmpbuffer;
> > > - leaf_d = bp->b_addr;
> > > - ichdr_s = *ichdr_d; /* struct copy */
> > > - ichdr_d->firstused = XFS_LBSIZE(mp);
> > > - ichdr_d->usedbytes = 0;
> > > - ichdr_d->count = 0;
> > > - ichdr_d->holes = 0;
> > > - ichdr_d->freemap[0].base = xfs_attr3_leaf_hdr_size(leaf_s);
> > > - ichdr_d->freemap[0].size = ichdr_d->firstused - ichdr_d->freemap[0].base;
> > > + memcpy(bp->b_addr, tmpbuffer, xfs_attr3_leaf_hdr_size(leaf_src));
> > > +
> > > + /* Initialise the incore headers */
> > > + ichdr_src = *ichdr_dst; /* struct copy */
> > > + ichdr_dst->firstused = XFS_LBSIZE(mp);
> > > + ichdr_dst->usedbytes = 0;
> > > + ichdr_dst->count = 0;
> > > + ichdr_dst->holes = 0;
> > > + ichdr_dst->freemap[0].base = xfs_attr3_leaf_hdr_size(leaf_src);
> > > + ichdr_dst->freemap[0].size = ichdr_dst->firstused -
> > > + ichdr_dst->freemap[0].base;
> > > +
> > > +
> > > + /* write the header back to initialise the underlying buffer */
> > > + xfs_attr3_leaf_hdr_to_disk(leaf_dst, ichdr_dst);
> >
> > I can see that the memcpy is necessary but again I'm having a hard time
> > understanding what field was messed up for moveents.
>
> moveents wasn't messed up - it was all the non-incore headers that
> were invalid (owner, uuid, blkno, etc) due to the zeroing of the tmp
> buffer and then only writing the incore header back to it after
> moveents. That's what the addition memcpy of the header fixes, and
> then the xfs_attr3_leaf_hdr_to_disk() call updates all the fields
> modified by initialisation so that before we start the in-core and
> "on-disk" structures are identical.

Reviewed-by: Ben Myers <bpm@sgi.com>