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

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Date:   Tue, 29 Nov 2022 19:59:14 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     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>
CC:     <djwong@...nel.org>, <david@...morbit.com>,
        <dan.j.williams@...el.com>, <akpm@...ux-foundation.org>
Subject: RE: [PATCH 0/2] fsdax,xfs: fix warning messages

[ 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

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.

> Shiyang Ruan (2):
>   fsdax,xfs: fix warning messages at dax_[dis]associate_entry()
>   fsdax,xfs: port unshare to fsdax
> 
>  fs/dax.c             | 166 ++++++++++++++++++++++++++++++-------------
>  fs/xfs/xfs_iomap.c   |   6 +-
>  fs/xfs/xfs_reflink.c |   8 ++-
>  include/linux/dax.h  |   2 +
>  4 files changed, 129 insertions(+), 53 deletions(-)
> 
> -- 
> 2.38.1