linux-kernel - Re: [PATCH] mm: get rid of WARN if failed to cow user pages

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Date:   Wed, 19 Feb 2020 09:58:19 +0800
From:   Murphy Zhou <jencce.kernel@...il.com>
To:     Jeff Moyer <jmoyer@...hat.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Murphy Zhou <jencce.kernel@...il.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Jia He <justin.he@....com>, Linux MM <linux-mm@...ck.org>,
        "Shutemov, Kirill" <kirill.shutemov@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: get rid of WARN if failed to cow user pages

On Tue, Feb 18, 2020 at 04:09:30PM -0500, Jeff Moyer wrote:
> Dan Williams <dan.j.williams@...el.com> writes:
> 
> > [ drop Ross, add Kirill, linux-mm, and lkml ]
> >
> > On Tue, Dec 24, 2019 at 9:42 PM Murphy Zhou <jencce.kernel@...il.com> wrote:
> >>
> >> By running xfstests with fsdax enabled, generic/437 always hits this
> >> warning[1] since this commit:
> >>
> >> commit 83d116c53058d505ddef051e90ab27f57015b025
> >> Author: Jia He <justin.he@....com>
> >> Date:   Fri Oct 11 22:09:39 2019 +0800
> >>
> >>     mm: fix double page fault on arm64 if PTE_AF is cleared
> >>
> >> Looking at the test program[2] generic/437 uses, it's pretty easy
> >> to hit this warning. Remove this WARN as it seems not necessary.
> >
> > This is not sufficient justification. Does this same test fail without
> > DAX? If not, why not? At a minimum you need to explain why this is not
> > indicating a problem.
> 
> I ran into this, too, and Kirill has posted a patch[1] to fix the issue.
> Note that it's a potential data corrupter, so just removing the warning
> is NOT the right approach.  :)

Agree :) Thanks!

> 
> -Jeff
> 
> [1] https://lore.kernel.org/linux-mm/20200218154151.13349-1-kirill.shutemov@linux.intel.com/T/#u
>