btrfs: run delayed iputs before committing

Delayed iputs means we can have final iputs of deleted inodes in the
queue, which could potentially generate a lot of pinned space that could
be free'd.  So before we decide to commit the transaction for ENOPSC
reasons, run the delayed iputs so that any potential space is free'd up.
If there is and we freed enough we can then commit the transaction and
potentially be able to make our reservation.
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent-tree.c

@@ -4952,6 +4952,15 @@ static void flush_space(struct btrfs_fs_info *fs_info,
 			ret = 0;
 		break;
 	case COMMIT_TRANS:
+		/*
+		 * If we have pending delayed iputs then we could free up a
+		 * bunch of pinned space, so make sure we run the iputs before
+		 * we do our pinned bytes check below.
+		 */
+		mutex_lock(&fs_info->cleaner_delayed_iput_mutex);
+		btrfs_run_delayed_iputs(fs_info);
+		mutex_unlock(&fs_info->cleaner_delayed_iput_mutex);
+
 		ret = may_commit_transaction(fs_info, space_info);
 		break;
 	default: