linux-kernel - [PATCH 5.11 17/44] btrfs: fix spurious free_space

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Date:   Mon,  8 Mar 2021 13:34:55 +0100
From:   gregkh@...uxfoundation.org
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Chris Murphy <lists@...orremedies.com>,
        Boris Burkov <boris@....io>, David Sterba <dsterba@...e.com>
Subject: [PATCH 5.11 17/44] btrfs: fix spurious free_space_tree remount warning

From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

From: Boris Burkov <boris@....io>

commit c55a4319c4f2c3ba0a385b1ebc454fa283cfe920 upstream.

The intended logic of the check is to catch cases where the desired
free_space_tree setting doesn't match the mounted setting, and the
remount is anything but ro->rw. However, it makes the mistake of
checking equality on a masked integer (btrfs_test_opt) against a boolean
(btrfs_fs_compat_ro).

If you run the reproducer:
  $ mount -o space_cache=v2 dev mnt
  $ mount -o remount,ro mnt

you would expect no warning, because the remount is not attempting to
change the free space tree setting, but we do see the warning.

To fix this, add explicit bool type casts to the condition.

I tested a variety of transitions:
sudo mount -o space_cache=v2 /dev/vg0/lv0 mnt/lol
(fst enabled)
mount -o remount,ro mnt/lol
(no warning, no fst change)
sudo mount -o remount,rw,space_cache=v1,clear_cache
(no warning, ro->rw)
sudo mount -o remount,rw,space_cache=v2 mnt
(warning, rw->rw with change)
sudo mount -o remount,ro mnt
(no warning, no fst change)
sudo mount -o remount,rw,space_cache=v2 mnt
(no warning, no fst change)

Reported-by: Chris Murphy <lists@...orremedies.com>
CC: stable@...r.kernel.org # 5.11
Signed-off-by: Boris Burkov <boris@....io>
Reviewed-by: David Sterba <dsterba@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/btrfs/super.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1919,8 +1919,8 @@ static int btrfs_remount(struct super_bl
 	btrfs_resize_thread_pool(fs_info,
 		fs_info->thread_pool_size, old_thread_pool_size);
 
-	if (btrfs_test_opt(fs_info, FREE_SPACE_TREE) !=
-	    btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE) &&
+	if ((bool)btrfs_test_opt(fs_info, FREE_SPACE_TREE) !=
+	    (bool)btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE) &&
 	    (!sb_rdonly(sb) || (*flags & SB_RDONLY))) {
 		btrfs_warn(fs_info,
 		"remount supports changing free space tree only from ro to rw");