FAILED: patch "[PATCH] btrfs: compression: don't try to compress if we don't have" failed to apply to 4.4-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f2165627319ffd33a6217275e5690b1ab5c45763 Mon Sep 17 00:00:00 2001
From: David Sterba <dsterba@suse.com>
Date: Mon, 14 Jun 2021 12:45:18 +0200
Subject: [PATCH] btrfs: compression: don't try to compress if we don't have
 enough pages

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>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index a2494c645681..e6eb20987351 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -629,7 +629,7 @@ static noinline int compress_file_range(struct async_chunk *async_chunk)
 	 * 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)) {
 		WARN_ON(pages);
 		pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
 		if (!pages) {