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From: Jan Kara <jack@suse.cz>
To: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Jan Kara <jack@suse.cz>,
	linux-nvdimm@lists.01.org,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Dave Chinner <david@fromorbit.com>,
	Lukas Czerner <lczerner@redhat.com>,
	linux-ext4@vger.kernel.org, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v4 0/2] ext4: fix DAX dma vs truncate/hole-punch
Date: Wed, 11 Jul 2018 10:17:41 +0200	[thread overview]
Message-ID: <20180711081741.lmr44sp4cmt3f6um@quack2.suse.cz> (raw)
In-Reply-To: <20180710191031.17919-1-ross.zwisler@linux.intel.com>

On Tue 10-07-18 13:10:29, Ross Zwisler wrote:
> Changes since v3:
>  * Added an ext4_break_layouts() call to ext4_insert_range() to ensure
>    that the {ext4,xfs}_break_layouts() calls have the same meaning.
>    (Dave, Darrick and Jan)

How about the occasional WARN_ON_ONCE you mention below. Were you able to
hunt them down?

								Honza
> ---
> 
> This series from Dan:
> 
> https://lists.01.org/pipermail/linux-nvdimm/2018-March/014913.html
> 
> added synchronization between DAX dma and truncate/hole-punch in XFS.
> This short series adds analogous support to ext4.
> 
> I've added calls to ext4_break_layouts() everywhere that ext4 removes
> blocks from an inode's map.
> 
> The timings in XFS are such that it's difficult to hit this race.  Dan
> was able to show the race by manually introducing delays in the direct
> I/O path.
> 
> For ext4, though, its trivial to hit this race, and a hit will result in
> a trigger of this WARN_ON_ONCE() in dax_disassociate_entry():
> 
>         WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
> 
> I've made an xfstest which tests all the paths where we now call
> ext4_break_layouts(). Each of the four paths easily hits this race many
> times in my test setup with the xfstest.  You can find that test here:
> 
> https://lists.01.org/pipermail/linux-nvdimm/2018-June/016435.html
> 
> With these patches applied, I've still seen occasional hits of the above
> WARN_ON_ONCE(), which tells me that we still have some work to do.  I'll
> continue looking at these more rare hits.
> 
> Ross Zwisler (2):
>   dax: dax_layout_busy_page() warn on !exceptional
>   ext4: handle layout changes to pinned DAX mappings
> 
>  fs/dax.c           | 10 +++++++++-
>  fs/ext4/ext4.h     |  1 +
>  fs/ext4/extents.c  | 17 +++++++++++++++++
>  fs/ext4/inode.c    | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>  fs/ext4/truncate.h |  4 ++++
>  5 files changed, 77 insertions(+), 1 deletion(-)
> 
> -- 
> 2.14.4
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR
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  parent reply	other threads:[~2018-07-11  8:17 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-10 19:10 Ross Zwisler
2018-07-10 19:10 ` [PATCH v4 1/2] dax: dax_layout_busy_page() warn on !exceptional Ross Zwisler
2018-08-10 19:52   ` Eric Sandeen
2018-08-10 20:33     ` Theodore Y. Ts'o
2018-08-11  2:10       ` Theodore Y. Ts'o
2018-08-13 10:12         ` Jan Kara
2018-08-13 12:46           ` Theodore Y. Ts'o
2018-08-24 15:44           ` Jan Kara
2018-08-27 16:09           ` Jan Kara
2018-07-10 19:10 ` [PATCH v4 2/2] ext4: handle layout changes to pinned DAX mappings Ross Zwisler
2018-07-11  8:17 ` Jan Kara [this message]
2018-07-11 15:41   ` [PATCH v4 0/2] ext4: fix DAX dma vs truncate/hole-punch Ross Zwisler
2018-07-25 22:28   ` Ross Zwisler
2018-07-27 16:28     ` Ross Zwisler
2018-08-06  3:55       ` Dave Chinner
2018-08-06 15:49         ` Christoph Hellwig
2018-08-06 22:25           ` Dave Chinner
2018-08-07  8:45       ` Jan Kara
2018-09-10 22:18         ` Eric Sandeen
2018-09-11 15:14           ` Jan Kara
2018-09-11 15:20             ` Jan Kara
2018-09-11 17:28               ` Theodore Y. Ts'o
2018-09-11 18:21                 ` Eric Sandeen
2018-07-31 19:44 ` Ross Zwisler

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