Received-SPF: pass (google.com: best guess record for domain of linux-ext4-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 15 Jan 2020 10:08:46 +0100
From:   Jan Kara <jack@suse.cz>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Jan Kara <jack@suse.cz>, Ritesh Harjani <riteshh@linux.ibm.com>,
        linux-ext4@vger.kernel.org, tytso@mit.edu
Subject: Re: [RFC 1/2] iomap: direct-io: Move inode_dio_begin before
 filemap_write_and_wait_range
Message-ID: <20200115090846.GB31450@quack2.suse.cz>
References: <cover.1578907890.git.riteshh@linux.ibm.com>
 <27607a16327fe9664f32d09abe565af0d1ae56c9.1578907891.git.riteshh@linux.ibm.com>
 <20200114163702.GA7127@infradead.org>
 <20200114171934.GB22081@quack2.suse.cz>
 <20200114182736.GA27370@infradead.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200114182736.GA27370@infradead.org>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-ext4-owner@vger.kernel.org
Precedence: bulk

On Tue 14-01-20 10:27:36, Christoph Hellwig wrote:
> On Tue, Jan 14, 2020 at 06:19:34PM +0100, Jan Kara wrote:
> > We want to detect in the writeback path whether there's direct IO (read)
> > currently running for the inode. Not for the writeback issued from
> > iomap_dio_rw() but for any arbitrary writeback that iomap_dio_rw() can be
> > racing with - so struct writeback_control won't help. Now if you want to
> > see the ugly details why this hack is needed, see my other email to Ritesh
> > in this thread with details of the race.
> 
> How do we get other writeback after iomap_dio_rw wrote everything out?

You create dirty page using mmap in the range read by iomap_dio_rw() and then
background writeback happens at unfortunate time... Email [1] has the exact
traces.

> Either way I'm trying to kill i_dio_count as it has all kinds of
> problems, see the patch sent out earlier today.

OK, I'll see that patch.

								Honza

[1] https://lore.kernel.org/linux-ext4/20200114094741.GC6466@quack2.suse.cz
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR