Re: FAILED: patch "[PATCH] btrfs: compression: don't try to compress if we don't have" failed to apply to 4.9-stable tree

[Sudip Mukherjee <sudipm.mukherjee@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 398 bytes --]

Hi Greg,

On Sun, Jul 11, 2021 at 02:21:22PM +0200, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 4.9-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>.

Here is the backport, will also apply to 4.4-stable.

--
Regards
Sudip

[-- Attachment #2: 0001-btrfs-compression-don-t-try-to-compress-if-we-don-t-.patch --]
[-- Type: text/x-diff, Size: 1571 bytes --]

From c2b38628ed59f7251f29e8cecb9f9d11c69c1ff0 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

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

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 4b671e5c33ce..a55d23a73cdb 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -484,7 +484,7 @@ static noinline void compress_file_range(struct inode *inode,
 	 * 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) {
-- 
2.30.2