btrfs: compression: don't try to compress if we don't have enough pages

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@vger.kernel.org # 4.4+
Signed-off-by: David Sterba <dsterba@suse.com>
[sudip: adjust context]
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index bf0e0e3e09c5d0d62a14d97ac1aa86c6a92b1dea..d29f4cf125d27ecfdc73448079df131bd7af0581 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -530,7 +530,7 @@ 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(inode, start, end)) {
+       if (nr_pages > 1 && inode_need_compress(inode, start, end)) {
                WARN_ON(pages);
                pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
                if (!pages) {