linux-kernel - [PATCH 4.4 47/47] btrfs: compression: dont try to compress if we dont have enough pages

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Message-Id: <20210726153824.455518827@linuxfoundation.org>
Date:   Mon, 26 Jul 2021 17:39:05 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, David Sterba <dsterba@...e.com>,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>
Subject: [PATCH 4.4 47/47] btrfs: compression: dont try to compress if we dont have enough pages

From: David Sterba <dsterba@...e.com>

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@...r.kernel.org # 4.4+
Signed-off-by: David Sterba <dsterba@...e.com>
[sudip: adjust context]
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/btrfs/inode.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -476,7 +476,7 @@ 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)) {
+	if (nr_pages > 1 && inode_need_compress(inode)) {
 		WARN_ON(pages);
 		pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
 		if (!pages) {