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

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

[Liu Bo]

This is an additional patch to
"Btrfs: memset to avoid stale content in btree node block".

This uses memset to initialize the unused space in a leaf to avoid
potential stale content, which may be incurred by pushing items
between sibling leaves.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
---
Tested with fstests '-g quick': no related panic or warning.

 fs/btrfs/ctree.c     | 14 --------------
 fs/btrfs/ctree.h     | 15 +++++++++++++++
 fs/btrfs/extent_io.c | 18 +++++++++++++-----
 3 files changed, 28 insertions(+), 19 deletions(-)

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index d1c56c9..f138cf7 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1729,20 +1729,6 @@ int btrfs_realloc_node(struct btrfs_trans_handle *trans,
 	return err;
 }
 
-/*
- * The leaf data grows from end-to-front in the node.
- * this returns the address of the start of the last item,
- * which is the stop of the leaf data stack
- */
-static inline unsigned int leaf_data_end(struct btrfs_root *root,
-					 struct extent_buffer *leaf)
-{
-	u32 nr = btrfs_header_nritems(leaf);
-	if (nr == 0)
-		return BTRFS_LEAF_DATA_SIZE(root);
-	return btrfs_item_offset_nr(leaf, nr - 1);
-}
-
 
 /*
  * search for key in the extent_buffer.  The items start at offset p,
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 33fe035..67d71c0 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2293,6 +2293,21 @@ static inline unsigned long btrfs_leaf_data(struct extent_buffer *l)
 	return offsetof(struct btrfs_leaf, items);
 }
 
+/*
+ * The leaf data grows from end-to-front in the node.
+ * this returns the address of the start of the last item,
+ * which is the stop of the leaf data stack
+ */
+static inline unsigned int leaf_data_end(struct btrfs_root *root,
+					 struct extent_buffer *leaf)
+{
+	u32 nr = btrfs_header_nritems(leaf);
+
+	if (nr == 0)
+		return BTRFS_LEAF_DATA_SIZE(root);
+	return btrfs_item_offset_nr(leaf, nr - 1);
+}
+
 /* struct btrfs_file_extent_item */
 BTRFS_SETGET_FUNCS(file_extent_type, struct btrfs_file_extent_item, type, 8);
 BTRFS_SETGET_STACK_FUNCS(stack_file_extent_disk_bytenr,
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 176f883..04a8e2a 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3721,8 +3721,10 @@ static noinline_for_stack int write_one_eb(struct extent_buffer *eb,
 	struct block_device *bdev = fs_info->fs_devices->latest_bdev;
 	struct extent_io_tree *tree = &BTRFS_I(fs_info->btree_inode)->io_tree;
 	u64 offset = eb->start;
+	u32 nritems;
 	unsigned long i, num_pages;
 	unsigned long bio_flags = 0;
+	unsigned long start, end;
 	int write_flags = (epd->sync_io ? WRITE_SYNC : 0) | REQ_META;
 	int ret = 0;
 
@@ -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);
+		end = btrfs_leaf_data(eb) +
+		      leaf_data_end(fs_info->tree_root, eb);
+		memset_extent_buffer(eb, 0, start, end - start);
 	}
 
 	for (i = 0; i < num_pages; i++) {
-- 
2.5.5

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

[David Sterba]

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>

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

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

[Liu Bo]

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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