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

[Greg KH <greg@kroah.com>]

On Tue, Feb 21, 2017 at 08:46:27AM -0500, Brian Foster wrote:
> commit fa7f138ac4c70dc00519c124cf7cd4862a0a5b0e upstream.
> 
> 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>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> CC: stable@vger.kernel.org # v4.8+
> ---
> 
> This is for stable... it fixes a latent regression exposed by
> d1908f52557b ("fs: break out of iomap_file_buffered_write on fatal
> signals"), which is to be backported to 4.8+ stable kernels.

For XFS patches, I need an explicit ack from the maintainer before
applying them, as per their instructions in the past...

thanks,

greg k-h