From: Matthew Wilcox <willy@infradead.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: linux-nvdimm <linux-nvdimm@lists.01.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"Balcer, Piotr" <piotr.balcer@intel.com>
Subject: Re: find_get_entries_tag regression bisected
Date: Tue, 26 Feb 2019 05:16:50 -0800 [thread overview]
Message-ID: <20190226131650.GE11592@bombadil.infradead.org> (raw)
In-Reply-To: <20190226120820.GB11592@bombadil.infradead.org>
On Tue, Feb 26, 2019 at 04:08:21AM -0800, Matthew Wilcox wrote:
> On Mon, Feb 25, 2019 at 09:03:00PM -0800, Dan Williams wrote:
> > On Sat, Feb 16, 2019 at 1:11 PM Matthew Wilcox <willy@infradead.org> wrote:
> > >
> > > On Sat, Feb 16, 2019 at 09:29:48AM -0800, Matthew Wilcox wrote:
> > > > On Sat, Feb 16, 2019 at 07:35:11AM -0800, Matthew Wilcox wrote:
> > > > > Another way to fix this would be to mask the address in dax_entry_mkclean(),
> > > > > but I think this is cleaner.
> > > >
> > > > That's clearly rubbish, dax_entry_mkclean() can't possibly mask the
> > > > address. It might be mis-aligned in another process. But ... if it's
> > > > misaligned in another process, dax_entry_mkclean() will only clean the first
> > > > PTE associated with the PMD; it won't clean the whole thing. I think we need
> > > > something like this:
> > >
> > > Nope, this isn't enough. It's _necessary_ to find the processes that
> > > have part of this PMD page mapped, but not the start of it. But it's
> > > not _sufficient_ because it'll still only mkclean the first PTE. So we
> > > need a loop. I'm feeling a bit over my head here. I may have a go at
> > > a fuller fix, but if someone else wants to have a go at it, be my guest!
> >
> > Nothing comes to mind outside of pseudo-reverting this conversion by
> > introducing a way to get back to the old semantics. If you don't see a
> > path forward, us mere Xarray-mortals stand no chance.
>
> This is a pre-existing bug. Fixing the regression is easy.
To be clear; I sent the regression fix a week ago in
20190216153511.GM12668@bombadil.infradead.org
I haven't tested it; I don't have a suitable setup right now.
The pre-existing bug is that if you have two tasks with the same
address range mapped, but one has it mapped with a PMD and the
other has it mapped with PTEs (maybe due to mapping only a subset
of the addresses), dax_entry_mkclean() won't clean the PTEs because
vma_interval_tree_foreach() won't find the VMA.
next prev parent reply other threads:[~2019-02-26 13:16 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-16 2:08 find_get_entries_tag regression bisected Dan Williams
2019-02-16 15:35 ` Matthew Wilcox
2019-02-16 17:29 ` Matthew Wilcox
2019-02-16 21:11 ` Matthew Wilcox
2019-02-26 5:03 ` Dan Williams
2019-02-26 12:08 ` Matthew Wilcox
2019-02-26 13:16 ` Matthew Wilcox [this message]
2019-02-27 18:16 ` Dan Williams
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