linux-ext4 - Re: dax pmd fault handler never returns to userspace

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Message-ID: <CAPcyv4g5LoOZH81JfB+xTKXs5cSxZogTfFUyQqq1U8h=aNrjuw@mail.gmail.com>
Date:	Wed, 18 Nov 2015 13:57:24 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Toshi Kani <toshi.kani@....com>
Cc:	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	linux-nvdimm <linux-nvdimm@...1.01.org>,
	Ross Zwisler <ross.zwisler@...el.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: dax pmd fault handler never returns to userspace

On Wed, Nov 18, 2015 at 1:33 PM, Toshi Kani <toshi.kani@....com> wrote:
> I am seeing a similar/same problem in my test.  I think the problem is that in
> case of a WP fault, wp_huge_pmd() -> __dax_pmd_fault() -> vmf_insert_pfn_pmd(),
> which is a no-op since the PMD is mapped already.  We need WP handling for this
> PMD map.
>
> If it helps, I have attached change for follow_trans_huge_pmd().  I have not
> tested much, though.

Interesting, I didn't get this far because my tests were crashing the
kernel.  I'll add this case the pmd fault test in ndctl.
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