From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-fsdevel-owner@vger.kernel.org>
Received: from verein.lst.de ([213.95.11.211]:32912 "EHLO newverein.lst.de"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1032266AbeEXSH7 (ORCPT <rfc822;linux-fsdevel@vger.kernel.org>);
        Thu, 24 May 2018 14:07:59 -0400
Date: Thu, 24 May 2018 20:13:33 +0200
From: Christoph Hellwig <hch@lst.de>
To: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>,
        "K.V, Aneesh" <aneesh.kumar@linux.vnet.ibm.com>,
        cluster-devel <cluster-devel@redhat.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: gfs2 iomap: BUG_ON(buffer_unmapped) in submit_bh_wbc
Message-ID: <20180524181333.GA24254@lst.de>
References: <CAHc6FU5a5E9K_AizwWkoPjb4cCWzqKspjc9YDVOzpCxcsDnKeA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAHc6FU5a5E9K_AizwWkoPjb4cCWzqKspjc9YDVOzpCxcsDnKeA@mail.gmail.com>
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

On Thu, May 24, 2018 at 08:05:03PM +0200, Andreas Gruenbacher wrote:
> Approach (1) is quite trivial:
> 
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1908,7 +1908,7 @@ iomap_to_bh(struct inode *inode, sector_t,
> struct buffer_head *bh,
>                 set_buffer_unwritten(bh);
>                 /* FALLTHRU */
>         case IOMAP_MAPPED:
> -               if (offset >= i_size_read(inode))
> +               if ((iomap->flags & IOMAP_F_NEW) || offset >=
> i_size_read(inode))
>                         set_buffer_new(bh);
>                 bh->b_blocknr = (iomap->addr + offset - iomap->offset) >>
>                                 inode->i_blkbits;
> 

This is the right thing to do.  We just didn't need to do it for XFS
as we'll never allocate normal blocks in write_begin.

You'll probably need similar tweaks in my new iomap write code, which
you're hopefully lookin into as well.