From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-fsdevel-owner@vger.kernel.org>
Received: from bombadil.infradead.org ([198.137.202.9]:47341 "EHLO
        bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1755794AbcKBO1r (ORCPT
        <rfc822;linux-fsdevel@vger.kernel.org>);
        Wed, 2 Nov 2016 10:27:47 -0400
Date: Wed, 2 Nov 2016 07:27:46 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        Dave Chinner <david@fromorbit.com>, Ted Tso <tytso@mit.edu>,
        linux-nvdimm@ml01.01.org
Subject: Re: [PATCH 02/11] ext4: Allow unaligned unlocked DAX IO
Message-ID: <20161102142746.GA18387@infradead.org>
References: <1478034381-19037-1-git-send-email-jack@suse.cz>
 <1478034381-19037-3-git-send-email-jack@suse.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1478034381-19037-3-git-send-email-jack@suse.cz>
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

On Tue, Nov 01, 2016 at 10:06:12PM +0100, Jan Kara wrote:
> Currently we don't allow unaligned writes without inode_lock. This is
> because zeroing of partial blocks could cause data corruption for racing
> unaligned writes to the same block. However DAX handles zeroing during
> block allocation and thus zeroing of partial blocks cannot race. Allow
> DAX unaligned IO to run without inode_lock.

DAX writes should always take the inode lock.  Without that you break
the expectations of existing applications that did not specify O_DIRECT.