[PATCH 5.10 040/593] btrfs: compression: dont try to compress if we dont have enough pages

From: Greg Kroah-Hartman
Date: Mon Jul 12 2021 - 02:38:15 EST

From: David Sterba <dsterba@xxxxxxxx>

commit f2165627319ffd33a6217275e5690b1ab5c45763 upstream.

The early check if we should attempt compression does not take into
account the number of input pages. It can happen that there's only one
page, eg. a tail page after some ranges of the BTRFS_MAX_UNCOMPRESSED
have been processed, or an isolated page that won't be converted to an
inline extent.

The single page would be compressed but a later check would drop it
again because the result size must be at least one block shorter than
the input. That can never work with just one page.

CC: stable@xxxxxxxxxxxxxxx # 4.4+
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

fs/btrfs/inode.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -547,7 +547,7 @@ again:
* inode has not been flagged as nocompress. This flag can
* change at any time if we discover bad compression ratios.
- if (inode_need_compress(BTRFS_I(inode), start, end)) {
+ if (nr_pages > 1 && inode_need_compress(BTRFS_I(inode), start, end)) {
pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
if (!pages) {