1 files changed, 12 insertions, 1 deletions

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index d366dd4664d0..c389c13f0f38 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -69,7 +69,7 @@ static struct file_system_type btrfs_fs_type;
 
 static int btrfs_remount(struct super_block *sb, int *flags, char *data);
 
-static const char *btrfs_decode_error(int errno)
+const char *btrfs_decode_error(int errno)
 {
         char *errstr = "unknown";
 
@@ -1651,6 +1651,17 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
 
                 sb->s_flags |= MS_RDONLY;
 
+                /*
+                 * Setting MS_RDONLY will put the cleaner thread to
+                 * sleep at the next loop if it's already active.
+                 * If it's already asleep, we'll leave unused block
+                 * groups on disk until we're mounted read-write again
+                 * unless we clean them up here.
+                 */
+                mutex_lock(&root->fs_info->cleaner_mutex);
+                btrfs_delete_unused_bgs(fs_info);
+                mutex_unlock(&root->fs_info->cleaner_mutex);
+
                 btrfs_dev_replace_suspend_for_unmount(fs_info);
                 btrfs_scrub_cancel(fs_info);
                 btrfs_pause_balance(fs_info);