btrfs: split out ro->rw and rw->ro helpers into their own functions

When we remount ro->rw or rw->ro we have some cleanup tasks that have to
be managed.  Split these out into their own function to make
btrfs_remount smaller.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/super.c

@@ -1676,6 +1676,115 @@ static inline void btrfs_remount_cleanup(struct btrfs_fs_info *fs_info,
 		btrfs_set_free_space_cache_v1_active(fs_info, cache_opt);
 }
 
+static int btrfs_remount_rw(struct btrfs_fs_info *fs_info)
+{
+	int ret;
+
+	if (BTRFS_FS_ERROR(fs_info)) {
+		btrfs_err(fs_info,
+			  "remounting read-write after error is not allowed");
+		return -EINVAL;
+	}
+
+	if (fs_info->fs_devices->rw_devices == 0)
+		return -EACCES;
+
+	if (!btrfs_check_rw_degradable(fs_info, NULL)) {
+		btrfs_warn(fs_info,
+			   "too many missing devices, writable remount is not allowed");
+		return -EACCES;
+	}
+
+	if (btrfs_super_log_root(fs_info->super_copy) != 0) {
+		btrfs_warn(fs_info,
+			   "mount required to replay tree-log, cannot remount read-write");
+		return -EINVAL;
+	}
+
+	/*
+	 * NOTE: when remounting with a change that does writes, don't put it
+	 * anywhere above this point, as we are not sure to be safe to write
+	 * until we pass the above checks.
+	 */
+	ret = btrfs_start_pre_rw_mount(fs_info);
+	if (ret)
+		return ret;
+
+	btrfs_clear_sb_rdonly(fs_info->sb);
+
+	set_bit(BTRFS_FS_OPEN, &fs_info->flags);
+
+	/*
+	 * If we've gone from readonly -> read-write, we need to get our
+	 * sync/async discard lists in the right state.
+	 */
+	btrfs_discard_resume(fs_info);
+
+	return 0;
+}
+
+static int btrfs_remount_ro(struct btrfs_fs_info *fs_info)
+{
+	/*
+	 * This also happens on 'umount -rf' or on shutdown, when the
+	 * filesystem is busy.
+	 */
+	cancel_work_sync(&fs_info->async_reclaim_work);
+	cancel_work_sync(&fs_info->async_data_reclaim_work);
+
+	btrfs_discard_cleanup(fs_info);
+
+	/* Wait for the uuid_scan task to finish */
+	down(&fs_info->uuid_tree_rescan_sem);
+	/* Avoid complains from lockdep et al. */
+	up(&fs_info->uuid_tree_rescan_sem);
+
+	btrfs_set_sb_rdonly(fs_info->sb);
+
+	/*
+	 * Setting SB_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.
+	 */
+	btrfs_delete_unused_bgs(fs_info);
+
+	/*
+	 * The cleaner task could be already running before we set the flag
+	 * BTRFS_FS_STATE_RO (and SB_RDONLY in the superblock).  We must make
+	 * sure that after we finish the remount, i.e. after we call
+	 * btrfs_commit_super(), the cleaner can no longer start a transaction
+	 * - either because it was dropping a dead root, running delayed iputs
+	 *   or deleting an unused block group (the cleaner picked a block
+	 *   group from the list of unused block groups before we were able to
+	 *   in the previous call to btrfs_delete_unused_bgs()).
+	 */
+	wait_on_bit(&fs_info->flags, BTRFS_FS_CLEANER_RUNNING, TASK_UNINTERRUPTIBLE);
+
+	/*
+	 * We've set the superblock to RO mode, so we might have made the
+	 * cleaner task sleep without running all pending delayed iputs. Go
+	 * through all the delayed iputs here, so that if an unmount happens
+	 * without remounting RW we don't end up at finishing close_ctree()
+	 * with a non-empty list of delayed iputs.
+	 */
+	btrfs_run_delayed_iputs(fs_info);
+
+	btrfs_dev_replace_suspend_for_unmount(fs_info);
+	btrfs_scrub_cancel(fs_info);
+	btrfs_pause_balance(fs_info);
+
+	/*
+	 * Pause the qgroup rescan worker if it is running. We don't want it to
+	 * be still running after we are in RO mode, as after that, by the time
+	 * we unmount, it might have left a transaction open, so we would leak
+	 * the transaction and/or crash.
+	 */
+	btrfs_qgroup_wait_for_completion(fs_info, false);
+
+	return btrfs_commit_super(fs_info);
+}
+
 static int btrfs_remount(struct super_block *sb, int *flags, char *data)
 {
 	struct btrfs_fs_info *fs_info = btrfs_sb(sb);
@@ -1729,120 +1838,14 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
 		}
 	}
 
-	if ((bool)(*flags & SB_RDONLY) == sb_rdonly(sb))
-		goto out;
-
-	if (*flags & SB_RDONLY) {
-		/*
-		 * this also happens on 'umount -rf' or on shutdown, when
-		 * the filesystem is busy.
-		 */
-		cancel_work_sync(&fs_info->async_reclaim_work);
-		cancel_work_sync(&fs_info->async_data_reclaim_work);
-
-		btrfs_discard_cleanup(fs_info);
-
-		/* wait for the uuid_scan task to finish */
-		down(&fs_info->uuid_tree_rescan_sem);
-		/* avoid complains from lockdep et al. */
-		up(&fs_info->uuid_tree_rescan_sem);
-
-		btrfs_set_sb_rdonly(sb);
-
-		/*
-		 * Setting SB_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.
-		 */
-		btrfs_delete_unused_bgs(fs_info);
-
-		/*
-		 * The cleaner task could be already running before we set the
-		 * flag BTRFS_FS_STATE_RO (and SB_RDONLY in the superblock).
-		 * We must make sure that after we finish the remount, i.e. after
-		 * we call btrfs_commit_super(), the cleaner can no longer start
-		 * a transaction - either because it was dropping a dead root,
-		 * running delayed iputs or deleting an unused block group (the
-		 * cleaner picked a block group from the list of unused block
-		 * groups before we were able to in the previous call to
-		 * btrfs_delete_unused_bgs()).
-		 */
-		wait_on_bit(&fs_info->flags, BTRFS_FS_CLEANER_RUNNING,
-			    TASK_UNINTERRUPTIBLE);
-
-		/*
-		 * We've set the superblock to RO mode, so we might have made
-		 * the cleaner task sleep without running all pending delayed
-		 * iputs. Go through all the delayed iputs here, so that if an
-		 * unmount happens without remounting RW we don't end up at
-		 * finishing close_ctree() with a non-empty list of delayed
-		 * iputs.
-		 */
-		btrfs_run_delayed_iputs(fs_info);
-
-		btrfs_dev_replace_suspend_for_unmount(fs_info);
-		btrfs_scrub_cancel(fs_info);
-		btrfs_pause_balance(fs_info);
-
-		/*
-		 * Pause the qgroup rescan worker if it is running. We don't want
-		 * it to be still running after we are in RO mode, as after that,
-		 * by the time we unmount, it might have left a transaction open,
-		 * so we would leak the transaction and/or crash.
-		 */
-		btrfs_qgroup_wait_for_completion(fs_info, false);
-
-		ret = btrfs_commit_super(fs_info);
-		if (ret)
-			goto restore;
-	} else {
-		if (BTRFS_FS_ERROR(fs_info)) {
-			btrfs_err(fs_info,
-				"Remounting read-write after error is not allowed");
-			ret = -EINVAL;
-			goto restore;
-		}
-		if (fs_info->fs_devices->rw_devices == 0) {
-			ret = -EACCES;
-			goto restore;
-		}
-
-		if (!btrfs_check_rw_degradable(fs_info, NULL)) {
-			btrfs_warn(fs_info,
-		"too many missing devices, writable remount is not allowed");
-			ret = -EACCES;
-			goto restore;
-		}
-
-		if (btrfs_super_log_root(fs_info->super_copy) != 0) {
-			btrfs_warn(fs_info,
-		"mount required to replay tree-log, cannot remount read-write");
-			ret = -EINVAL;
-			goto restore;
-		}
-
-		/*
-		 * NOTE: when remounting with a change that does writes, don't
-		 * put it anywhere above this point, as we are not sure to be
-		 * safe to write until we pass the above checks.
-		 */
-		ret = btrfs_start_pre_rw_mount(fs_info);
-		if (ret)
-			goto restore;
-
-		btrfs_clear_sb_rdonly(sb);
-
-		set_bit(BTRFS_FS_OPEN, &fs_info->flags);
+	ret = 0;
+	if (!sb_rdonly(sb) && (*flags & SB_RDONLY))
+		ret = btrfs_remount_ro(fs_info);
+	else if (sb_rdonly(sb) && !(*flags & SB_RDONLY))
+		ret = btrfs_remount_rw(fs_info);
+	if (ret)
+		goto restore;
 
-		/*
-		 * If we've gone from readonly -> read/write, we need to get
-		 * our sync/async discard lists in the right state.
-		 */
-		btrfs_discard_resume(fs_info);
-	}
-out:
 	/*
 	 * We need to set SB_I_VERSION here otherwise it'll get cleared by VFS,
 	 * since the absence of the flag means it can be toggled off by remount.