Re: [PATCH 1/4] xfs: clear delalloc and cache on buffered write failure

[Brian Foster <bfoster@redhat.com>]

On Thu, Feb 16, 2017 at 12:24:04PM -0800, Christoph Hellwig wrote:
> On Tue, Feb 14, 2017 at 08:03:06AM -0500, Brian Foster wrote:
> > The buffered write failure handling code in
> > xfs_file_iomap_end_delalloc() has a couple minor problems. First, if
> > written == 0, start_fsb is not rounded down and it fails to kill off a
> > delalloc block if the start offset is block unaligned. This results in a
> > lingering delalloc block and broken delalloc block accounting detected
> > at unmount time. Fix this by rounding down start_fsb in the unlikely
> > event that written == 0.
> > 
> > Second, it is possible for a failed overwrite of a delalloc extent to
> > leave dirty pagecache around over a hole in the file. This is because is
> > possible to hit ->iomap_end() on write failure before the iomap code has
> > attempted to allocate pagecache, and thus has no need to clean it up. If
> > the targeted delalloc extent was successfully written by a previous
> > write, however, then it does still have dirty pages when ->iomap_end()
> > punches out the underlying blocks. This ultimately results in writeback
> > over a hole. To fix this problem, unconditionally punch out the
> > pagecache from XFS before the associated delalloc range.
> > 
> > Signed-off-by: Brian Foster <bfoster@redhat.com>
> > ---
> >  fs/xfs/xfs_iomap.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> > index e0bc290..e2fbed4 100644
> > --- a/fs/xfs/xfs_iomap.c
> > +++ b/fs/xfs/xfs_iomap.c
> > @@ -1079,6 +1079,8 @@ xfs_file_iomap_end_delalloc(
> >  	int			error = 0;
> >  
> >  	start_fsb = XFS_B_TO_FSB(mp, offset + written);
> > +	if (unlikely(!written))
> > +		start_fsb = XFS_B_TO_FSBT(mp, offset);
> 
> nitpick: use if/else here and maybe add a comment?
> 

Sure..

Brian

> Otherwise looks fine:
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
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