Re: [PATCH v2] xfs: truncate delalloc extents when IO fails in writeback

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

On Fri, Mar 05, 2010 at 01:00:42PM +1100, Dave Chinner wrote:
> 
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> We currently use block_invalidatepage() to clean up pages where I/O
> fails in ->writepage(). Unfortunately, if the page has delalloc
> regions on it, we fail to remove the delalloc regions when we
> invalidate the page.  This can result in tripping a BUG() in
> xfs_get_blocks() later on if a direct IO read is done on that same
> region - the delalloc extent is returned when none is supposed to be
> there.
> 
> Fix this by truncating away the delalloc regions on the page before
> invalidating it. Because they are delalloc, we can do this without
> needing a transaction. Indeed - if we get ENOSPC errors, we have to
> be able to do this truncation without a transaction as there is
> no space left for block reservation (typically why we see a ENOSPC
> in writeback).

Looks good.  I also like the new assert to ensure no blocks actually
get freed.

Reviewed-by: Christoph Hellwig <hch@xxxxxx>