linux-kernel - Re: [PATCH 0/2] fsdax,xfs: fix warning messages

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Date:   Wed, 30 Nov 2022 15:58:31 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Darrick J. Wong" <djwong@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Shiyang Ruan <ruansy.fnst@...itsu.com>,
        <linux-kernel@...r.kernel.org>, <linux-xfs@...r.kernel.org>,
        <nvdimm@...ts.linux.dev>, <linux-fsdevel@...r.kernel.org>,
        <david@...morbit.com>
Subject: Re: [PATCH 0/2] fsdax,xfs: fix warning messages

Darrick J. Wong wrote:
> On Wed, Nov 30, 2022 at 01:48:59PM -0800, Dan Williams wrote:
> > Andrew Morton wrote:
> > > On Tue, 29 Nov 2022 19:59:14 -0800 Dan Williams <dan.j.williams@...el.com> wrote:
> > > 
> > > > [ add Andrew ]
> > > > 
> > > > Shiyang Ruan wrote:
> > > > > Many testcases failed in dax+reflink mode with warning message in dmesg.
> > > > > This also effects dax+noreflink mode if we run the test after a
> > > > > dax+reflink test.  So, the most urgent thing is solving the warning
> > > > > messages.
> > > > > 
> > > > > Patch 1 fixes some mistakes and adds handling of CoW cases not
> > > > > previously considered (srcmap is HOLE or UNWRITTEN).
> > > > > Patch 2 adds the implementation of unshare for fsdax.
> > > > > 
> > > > > With these fixes, most warning messages in dax_associate_entry() are
> > > > > gone.  But honestly, generic/388 will randomly failed with the warning.
> > > > > The case shutdown the xfs when fsstress is running, and do it for many
> > > > > times.  I think the reason is that dax pages in use are not able to be
> > > > > invalidated in time when fs is shutdown.  The next time dax page to be
> > > > > associated, it still remains the mapping value set last time.  I'll keep
> > > > > on solving it.
> > > > > 
> > > > > The warning message in dax_writeback_one() can also be fixed because of
> > > > > the dax unshare.
> > > > 
> > > > Thank you for digging in on this, I had been pinned down on CXL tasks
> > > > and worried that we would need to mark FS_DAX broken for a cycle, so
> > > > this is timely.
> > > > 
> > > > My only concern is that these patches look to have significant collisions with
> > > > the fsdax page reference counting reworks pending in linux-next. Although,
> > > > those are still sitting in mm-unstable:
> > > > 
> > > > http://lore.kernel.org/r/20221108162059.2ee440d5244657c4f16bdca0@linux-foundation.org
> > > 
> > > As far as I know, Dan's "Fix the DAX-gup mistake" series is somewhat
> > > stuck.  Jan pointed out:
> > > 
> > > https://lore.kernel.org/all/20221109113849.p7pwob533ijgrytu@quack3/T/#u
> > > 
> > > or have Jason's issues since been addressed?
> > 
> > No, they have not. I do think the current series is a step forward, but
> > given the urgency remains low for the time being (CXL hotplug use case
> > further out, no known collisions with ongoing folio work, and no
> > MEMORY_DEVICE_PRIVATE users looking to build any conversions on top for
> > 6.2) I am ok to circle back for 6.3 for that follow on work to be
> > integrated.
> > 
> > > > My preference would be to move ahead with both in which case I can help
> > > > rebase these fixes on top. In that scenario everything would go through
> > > > Andrew.
> > > > 
> > > > However, if we are getting too late in the cycle for that path I think
> > > > these dax-fixes take precedence, and one more cycle to let the page
> > > > reference count reworks sit is ok.
> > > 
> > > That sounds a decent approach.  So we go with this series ("fsdax,xfs:
> > > fix warning messages") and aim at 6.3-rc1 with "Fix the DAX-gup
> > > mistake"?
> > > 
> > 
> > Yeah, that's the path of least hassle.
> 
> Sounds good.  I still want to see patch 1 of this series broken up into
> smaller pieces though.  Once the series goes through review, do you want
> me to push the fixes to Linus, seeing as xfs is the only user of this
> functionality?

Yes, that was my primary feedback as well, and merging through xfs makes
sense to me.