linux-kernel - Re: [PATCH 01/14] iomap: iomap that extends beyond EOF should be marked dirty

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Date:   Thu, 17 Oct 2019 18:02:20 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Matthew Bobrowski <mbobrowski@...browski.org>
Cc:     Dave Chinner <david@...morbit.com>, Christoph Hellwig <hch@....de>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, Dave Chinner <dchinner@...hat.com>
Subject: Re: [PATCH 01/14] iomap: iomap that extends beyond EOF should be
 marked dirty

On Fri, Oct 18, 2019 at 10:08:14AM +1100, Matthew Bobrowski wrote:
> On Fri, Oct 18, 2019 at 08:56:13AM +1100, Dave Chinner wrote:
> > On Thu, Oct 17, 2019 at 11:39:17AM -0700, Darrick J. Wong wrote:
> > > On Thu, Oct 17, 2019 at 07:56:11PM +0200, Christoph Hellwig wrote:
> > > > From: Dave Chinner <dchinner@...hat.com>
> > > > 
> > > > When doing a direct IO that spans the current EOF, and there are
> > > > written blocks beyond EOF that extend beyond the current write, the
> > > > only metadata update that needs to be done is a file size extension.
> > > > 
> > > > However, we don't mark such iomaps as IOMAP_F_DIRTY to indicate that
> > > > there is IO completion metadata updates required, and hence we may
> > > > fail to correctly sync file size extensions made in IO completion
> > > > when O_DSYNC writes are being used and the hardware supports FUA.
> > > > 
> > > > Hence when setting IOMAP_F_DIRTY, we need to also take into account
> > > > whether the iomap spans the current EOF. If it does, then we need to
> > > > mark it dirty so that IO completion will call generic_write_sync()
> > > > to flush the inode size update to stable storage correctly.
> > > > 
> > > > Signed-off-by: Dave Chinner <dchinner@...hat.com>
> > > > Signed-off-by: Christoph Hellwig <hch@....de>
> > > 
> > > Looks ok, but need fixes tag.  Also, might it be wise to split off the
> > > ext4 section into a separate patch so that it can be backported
> > > separately?
> > 
> > I 've done a bit more digging on this, and the ext4 part is not
> > needed for DAX as IOMAP_F_DIRTY is only used in the page fault path
> > and hence can't change the file size. As such, this only affects
> > direct IO. Hence the ext4 hunk can be added to the ext4 iomap-dio
> > patchset that is being developed rather than being in this patch.
> 
> Noted, thanks Dave. I've incorporated the ext4 related change into my patch
> series.

Ok, I've dropped the ext4 hunk from my branch.

--D

> --<M>--