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

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Date:	Thu, 10 Dec 2015 09:54:58 -0700
From:	Ross Zwisler <ross.zwisler@...ux.intel.com>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Dave Chinner <david@...morbit.com>, xfs@....sgi.com,
	Brian Foster <bfoster@...hat.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jeff Moyer <jmoyer@...hat.com>
Subject: Re: xfstests failures with xfs, dax and v4.4-rc3

On Wed, Dec 02, 2015 at 02:39:32PM -0700, Ross Zwisler wrote:
> 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@...morbit.com
> > 
> > xfs: Don't use reserved blocks for data blocks with DAX
> > 
> > From: Dave Chinner <dchinner@...hat.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@...hat.com>
> 
> Tested-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> 
> I've verified that this fixes all three failing xfstests reported in this mail.
> Thanks!

Hey Dave,

Are you planning on pushing this fix for v4.4?

- Ross
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