linux-kernel - Re: [PATCH v2 1/3] mm: Trigger bug on if a section is not found in __section

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Message-ID: <20190626065751.GK17798@dhcp22.suse.cz>
Date:   Wed, 26 Jun 2019 08:57:51 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Alastair D'Silva <alastair@...ilva.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Oscar Salvador <osalvador@...e.de>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Baoquan He <bhe@...hat.com>,
        Wei Yang <richard.weiyang@...il.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 1/3] mm: Trigger bug on if a section is not found in
 __section_nr

On Wed 26-06-19 16:27:30, Alastair D'Silva wrote:
> On Wed, 2019-06-26 at 08:21 +0200, Michal Hocko wrote:
> > On Wed 26-06-19 16:11:21, Alastair D'Silva wrote:
> > > From: Alastair D'Silva <alastair@...ilva.org>
> > > 
> > > If a memory section comes in where the physical address is greater
> > > than
> > > that which is managed by the kernel, this function would not
> > > trigger the
> > > bug and instead return a bogus section number.
> > > 
> > > This patch tracks whether the section was actually found, and
> > > triggers the
> > > bug if not.
> > 
> > Why do we want/need that? In other words the changelog should contina
> > WHY and WHAT. This one contains only the later one.
> >  
> 
> Thanks, I'll update the comment.
> 
> During driver development, I tried adding peristent memory at a memory
> address that exceeded the maximum permissable address for the platform.
> 
> This caused __section_nr to silently return bogus section numbers,
> rather than complaining.

OK, I see, but is an additional code worth it for the non-development
case? I mean why should we be testing for something that shouldn't
happen normally? Is it too easy to get things wrong or what is the
underlying reason to change it now?

-- 
Michal Hocko
SUSE Labs