From: Jan Kara Subject: Re: [PATCH v4 0/2] ext4: fix DAX dma vs truncate/hole-punch Date: Wed, 11 Jul 2018 10:17:41 +0200 Message-ID: <20180711081741.lmr44sp4cmt3f6um@quack2.suse.cz> References: <20180710191031.17919-1-ross.zwisler@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Jan Kara , linux-nvdimm-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org, "Darrick J. Wong" , Dave Chinner , Lukas Czerner , linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Christoph Hellwig To: Ross Zwisler Return-path: Content-Disposition: inline In-Reply-To: <20180710191031.17919-1-ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" List-Id: linux-ext4.vger.kernel.org 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 SUSE Labs, CR