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Re: [PATCH 06/11] xfs: fully initialise temp leaf in xfs_attr3_leaf_unba

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 06/11] xfs: fully initialise temp leaf in xfs_attr3_leaf_unbalance
From: Ben Myers <bpm@xxxxxxx>
Date: Thu, 23 May 2013 17:51:22 -0500
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130522235450.GO29466@dastard>
References: <1369123330-9579-1-git-send-email-david@xxxxxxxxxxxxx> <1369123330-9579-7-git-send-email-david@xxxxxxxxxxxxx> <20130522205059.GP20028@xxxxxxx> <20130522235450.GO29466@dastard>
User-agent: Mutt/1.5.20 (2009-06-14)
On Thu, May 23, 2013 at 09:54:50AM +1000, Dave Chinner wrote:
> On Wed, May 22, 2013 at 03:50:59PM -0500, Ben Myers wrote:
> > On Tue, May 21, 2013 at 06:02:05PM +1000, Dave Chinner wrote:
> > > From: Dave Chinner <dchinner@xxxxxxxxxx>
> > > 
> > > xfs_attr3_leaf_unbalance() uses a temporary buffer for recombining
> > > the entries in two leaves when the destination leaf requires
> > > compaction. The temporary buffer ends up being copied back over the
> > > original destination buffer, so the header in the temporary buffer
> > > needs to contain all the information that is in the destination
> > > buffer.
> > > 
> > > To make sure the temporary buffer is fully initialised, once we've
> > > set up the temporary incore header appropriately, write is back to
> > > the temporary buffer before starting to move entries around.
> > > 
> > > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> > >
> > > ---
> > >  fs/xfs/xfs_attr_leaf.c |   16 +++++++++++++---
> > >  1 file changed, 13 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/fs/xfs/xfs_attr_leaf.c b/fs/xfs/xfs_attr_leaf.c
> > > index 0bce1b3..79ece72 100644
> > > --- a/fs/xfs/xfs_attr_leaf.c
> > > +++ b/fs/xfs/xfs_attr_leaf.c
> > > @@ -2181,14 +2181,24 @@ xfs_attr3_leaf_unbalance(
> > >           struct xfs_attr_leafblock *tmp_leaf;
> > >           struct xfs_attr3_icleaf_hdr tmphdr;
> > >  
> > > -         tmp_leaf = kmem_alloc(state->blocksize, KM_SLEEP);
> > > -         memset(tmp_leaf, 0, state->blocksize);
> > > -         memset(&tmphdr, 0, sizeof(tmphdr));
> > > +         tmp_leaf = kmem_zalloc(state->blocksize, KM_SLEEP);
> > > +
> > > +         /*
> > > +          * Copy the header into the temp leaf so that all the stuff
> > > +          * not in the incore header is present and gets copied back in
> > > +          * once we've moved all the entries.
> > > +          */
> > > +         memcpy(tmp_leaf, save_leaf, xfs_attr3_leaf_hdr_size(save_leaf));
> > >  
> > > +         memset(&tmphdr, 0, sizeof(tmphdr));
> > >           tmphdr.magic = savehdr.magic;
> > >           tmphdr.forw = savehdr.forw;
> > >           tmphdr.back = savehdr.back;
> > >           tmphdr.firstused = state->blocksize;
> > > +
> > > +         /* write the header to the temp buffer to initialise it */
> > > +         xfs_attr3_leaf_hdr_to_disk(tmp_leaf, &tmphdr);
> > > +
> > 
> > Hrm.  It seemed like the memset 0 for the incore temp header should have 
> > been
> > enough for the purposes of moveents.  Why did you have to add this 
> > additional
> > hdr_to_disk?
> 
> Because we've modified the tmphdr so it is different to what is in
> the tmp_leaf, and I'm being paranoid and not making any assumptions
> that a callee doesn't reread the tmphdr from the tmp_leaf.
> 
> i.e. I'm initialising both the on-disk and the incore headers to
> be identical before we do anything else. Once bitten, twice shy.

Reviewed-by: Ben Myers <bpm@xxxxxxx>

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