Re: xfstests failures with xfs, dax and v4.4-rc3

[Ross Zwisler <ross.zwisler@linux.intel.com>]

On Thu, Dec 03, 2015 at 07:45:02AM +1100, Dave Chinner wrote:
> On Thu, Dec 03, 2015 at 07:29:10AM +1100, Dave Chinner wrote:
> > On Wed, Dec 02, 2015 at 11:34:38AM -0700, Ross Zwisler wrote:
> > > I'm hitting a few more test failures in my testing setup with v4.4-rc3, xfs
> > > and DAX.  My test setup is a pair of 4GiB PMEM partitions in a KVM virtual
> > > machine.  Here are the failures:
> > 
> > Which are caused by commit 1ca1915 ("xfs: Don't use unwritten extents
> > for DAX") because of this code for unwritten extent conversion in
> > get_blocks:
> > 
> > 	tp->t_flags |= XFS_TRANS_RESERVE;
> > 
> > It's a minor problem compared to all the other issues DAX has right
> > now, so I ignored it to get the bigger problem solved first.
> 
> Patch to fix the problem below.
> 
> -Dave.
> -- 
> Dave Chinner
> david@fromorbit.com
> 
> xfs: Don't use reserved blocks for data blocks with DAX
> 
> From: Dave Chinner <dchinner@redhat.com>
> 
> Commit 1ca1915 ("xfs: Don't use unwritten extents for DAX") enabled
> the DAX allocation call to dip into the reserve pool in case it was
> converting unwritten extents rather than allocating blocks. This was
> a direct copy of the unwritten extent conversion code, but had an
> unintended side effect of allowing normal data block allocation to
> use the reserve pool. Hence normal block allocation could deplete
> the reserve pool and prevent unwritten extent conversion at ENOSPC,
> hence violating fallocate guarantees on preallocated space.
> 
> Fix it by checking whether the incoming map from __xfs_get_blocks()
> spans an unwritten extent and only use the reserve pool if the
> allocation covers an unwritten extent.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

Tested-by: Ross Zwisler <ross.zwisler@linux.intel.com>

I've verified that this fixes all three failing xfstests reported in this mail.
Thanks!