linux-ext4 - Re: [PATCH 02/11] ext4: Allow unaligned unlocked DAX IO

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Message-ID: <20161103235544.GG24234@quack2.suse.cz>
Date:   Fri, 4 Nov 2016 00:55:44 +0100
From:   Jan Kara <jack@...e.cz>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Dave Chinner <david@...morbit.com>,
        Ted Tso <tytso@....edu>, linux-nvdimm@...1.01.org
Subject: Re: [PATCH 02/11] ext4: Allow unaligned unlocked DAX IO

On Wed 02-11-16 07:27:46, Christoph Hellwig wrote:
> 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.

Yeah, actually this patch has no practical effect since later iomap
conversion just effectively reverts this patch and I didn't realize it.
I'll just drop it. Thanks.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR
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