btrfs: explictly delete unused block groups in close_ctree and ro-remount

The cleaner thread may already be sleeping by the time we enter
close_ctree.  If that's the case, we'll skip removing any unused
block groups queued for removal, even during a normal umount.
They'll be cleaned up automatically at next mount, but users
expect a umount to be a clean synchronization point, especially
when used on thin-provisioned storage with -odiscard.  We also
explicitly remove unused block groups in the ro-remount path
for the same reason.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Tested-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>

2 files changed, 20 insertions, 0 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 84cbbb2d562e..053109ba26b7 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3767,6 +3767,15 @@ void close_ctree(struct btrfs_root *root)
         cancel_work_sync(&fs_info->async_reclaim_work);
 
         if (!(fs_info->sb->s_flags & MS_RDONLY)) {
+                /*
+                 * If the cleaner thread is stopped and there are
+                 * block groups queued for removal, the deletion will be
+                 * skipped when we quit the cleaner thread.
+                 */
+                mutex_lock(&root->fs_info->cleaner_mutex);
+                btrfs_delete_unused_bgs(root->fs_info);
+                mutex_unlock(&root->fs_info->cleaner_mutex);
+
                 ret = btrfs_commit_super(root);
                 if (ret)
                         btrfs_err(fs_info, "commit super ret %d", ret);
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index cd7ef34d2dce..a1077e0ffaa8 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1650,6 +1650,17 @@ 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);