btrfs: only invalidate btree inode pages after all ebs are released

In close_ctree(), we call invalidate_inode_pages2() to invalidate all
pages from btree inode.

But the problem is, it never returns 0, but always -EBUSY.

The problem is that we are still holding all the essential tree root
nodes, thus pages holding those tree blocks can not be invalidated thus
invalidate_inode_pages2() always returns -EBUSY.

This is also against the error cleanup path of open_ctree(), which
properly frees all root pointers before calling invalidate_inode_pages().

So fix the order by delaying invalidate_inode_pages2() until we have
freed all root pointers.

Reviewed-by: Anand Jain <asj@kernel.org>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: adam900710

fs/btrfs/disk-io.c

@@ -4434,20 +4434,20 @@ void __cold close_ctree(struct btrfs_fs_info *fs_info)
 
 	btrfs_put_block_group_cache(fs_info);
 
-	/*
-	 * we must make sure there is not any read request to
-	 * submit after we stopping all workers.
-	 */
-	invalidate_inode_pages2(fs_info->btree_inode->i_mapping);
-	btrfs_stop_all_workers(fs_info);
-
 	/* We shouldn't have any transaction open at this point */
 	warn_about_uncommitted_trans(fs_info);
 
 	clear_bit(BTRFS_FS_OPEN, &fs_info->flags);
 	free_root_pointers(fs_info, true);
 	btrfs_free_fs_roots(fs_info);
 
+	/*
+	 * We must make sure there is not any read request to
+	 * submit after we stop all workers.
+	 */
+	invalidate_inode_pages2(fs_info->btree_inode->i_mapping);
+	btrfs_stop_all_workers(fs_info);
+
 	/*
 	 * We must free the block groups after dropping the fs_roots as we could
 	 * have had an IO error and have left over tree log blocks that aren't