2020-01-15 06:04:05

by Dan Williams

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 <[email protected]> wrote:
>
> By running xfstests with fsdax enabled, generic/437 always hits this
> warning[1] since this commit:
>
> commit 83d116c53058d505ddef051e90ab27f57015b025
> Author: Jia He <[email protected]>
> 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.

2020-02-18 21:10:34

by Jeff Moyer

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

Dan Williams <[email protected]> writes:

> [ drop Ross, add Kirill, linux-mm, and lkml ]
>
> On Tue, Dec 24, 2019 at 9:42 PM Murphy Zhou <[email protected]> wrote:
>>
>> By running xfstests with fsdax enabled, generic/437 always hits this
>> warning[1] since this commit:
>>
>> commit 83d116c53058d505ddef051e90ab27f57015b025
>> Author: Jia He <[email protected]>
>> 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. :)

-Jeff

[1] https://lore.kernel.org/linux-mm/[email protected]/T/#u

2020-02-19 01:58:52

by Murphy Zhou

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 <[email protected]> writes:
>
> > [ drop Ross, add Kirill, linux-mm, and lkml ]
> >
> > On Tue, Dec 24, 2019 at 9:42 PM Murphy Zhou <[email protected]> wrote:
> >>
> >> By running xfstests with fsdax enabled, generic/437 always hits this
> >> warning[1] since this commit:
> >>
> >> commit 83d116c53058d505ddef051e90ab27f57015b025
> >> Author: Jia He <[email protected]>
> >> 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/[email protected]/T/#u
>