Re: correct use of vmtruncate()?

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

On Tue, Apr 29, 2008 at 10:10:59AM -0700, Zach Brown wrote:
> 
> > The obvious fix for this is that block_write_begin() and
> > friends should be calling ->setattr to do the truncation and hence
> > follow normal convention for truncating blocks off an inode.
> > However, even that appears to have thorns. e.g. in XFS we hold the
> > iolock exclusively when we call block_write_begin(), but it is not
> > held in all cases where ->setattr is currently called. Hence calling
> > ->setattr from block_write_begin in this failure case will deadlock
> > unless we also pass a "nolock" flag as well. XFS already
> > supports this (e.g. see the XFS fallocate implementation) but no other
> > filesystem does (some probably don't need to).
> 
> This paragraph in particular reminds me of an outstanding bug with
> O_DIRECT and ext*.  It isn't truncating partial allocations when a dio
> fails with ENOSPC.  This was noticed by a user who saw that fsck found
> bocks outside i_size in the file that saw ENOSPC if they tried to
> unmount and check the volume after the failed write.

This patch should be the fix I guess
	http://lkml.org/lkml/2006/12/18/103

-aneesh