Re: [PATCH] Btrfs: memset to avoid stale content in btree leaf

[Liu Bo <bo.li.liu@oracle.com>]

On Mon, Sep 26, 2016 at 06:54:44PM +0200, David Sterba wrote:
> On Fri, Sep 23, 2016 at 01:44:44PM -0700, Liu Bo wrote:
> > @@ -3732,15 +3734,21 @@ static noinline_for_stack int write_one_eb(struct extent_buffer *eb,
> >  	if (btrfs_header_owner(eb) == BTRFS_TREE_LOG_OBJECTID)
> >  		bio_flags = EXTENT_BIO_TREE_LOG;
> >  
> > -	/* set btree node beyond nritems with 0 to avoid stale content */
> > +	/* set btree blocks beyond nritems with 0 to avoid stale content. */
> > +	nritems = btrfs_header_nritems(eb);
> >  	if (btrfs_header_level(eb) > 0) {
> > -		u32 nritems;
> > -		unsigned long end;
> > -
> > -		nritems = btrfs_header_nritems(eb);
> >  		end = btrfs_node_key_ptr_offset(nritems);
> >  
> >  		memset_extent_buffer(eb, 0, end, eb->len - end);
> > +	} else {
> > +		/*
> > +		 * leaf:
> > +		 * header 0 1 2 .. N ... data_N .. data_2 data_1 data_0
> > +		 */
> > +		start = btrfs_item_nr_offset(nritems);
> 
> So, AFAICS this also works for empty root nodes (nritems == 0). It's
> hidden in leaf_data_end that actually looks at nritems and decides.
> 
> Reviewed-by: David Sterba <dsterba@suse.com>

Yeah, you're right, case (nritems == 0) has already been taken care in this patch.

Thanks a lot for reviewing it.

Thanks,

-liubo
> 
> > +		end = btrfs_leaf_data(eb) +
> > +		      leaf_data_end(fs_info->tree_root, eb);
> > +		memset_extent_buffer(eb, 0, start, end - start);
> --
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