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

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Message-ID: <CAPcyv4hMPh0C+_OV+vuiYQikb8ZvRanna4vXfKN=10yrAyCjDA@mail.gmail.com>
Date:   Tue, 14 Jan 2020 22:02:34 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Murphy Zhou <jencce.kernel@...il.com>
Cc:     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

[ 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.