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

Matthew Bobrowski
2019-10-17T23:08:26Z

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@redhat.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@redhat.com>
> > > Signed-off-by: Christoph Hellwig <hch@lst.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.

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