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

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Date:   Wed, 30 Nov 2022 13:27:25 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     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>,
        <djwong@...nel.org>, <david@...morbit.com>
Subject: Re: [PATCH 0/2] fsdax,xfs: fix warning messages

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?

> 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"?