linux-kernel - Re: [PATCH] mm: page_alloc: ignore init_on

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Message-ID: <CA+fCnZeC8AWearU9CQaYrFM-ZCUaQpX1e7vBkRMNtqqf_=ucGA@mail.gmail.com>
Date:   Fri, 26 Mar 2021 16:00:34 +0100
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     David Hildenbrand <david@...hat.com>,
        Sergei Trofimovich <slyfox@...too.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] mm: page_alloc: ignore init_on_free=1 for page alloc

On Fri, Mar 26, 2021 at 2:49 PM David Hildenbrand <david@...hat.com> wrote:
>
> > I observed use of poisoned pages as the crash on ia64 booted with
> > init_on_free=1 init_on_alloc=1 (CONFIG_PAGE_POISONING=y config).
> > There pmd page contained 0xaaaaaaaa poison pages and led to early crash.
> >
> > The change drops the assumption that init_on_free=1 guarantees free
> > pages to contain zeros.
> >
> > Alternative would be to make interaction between runtime poisoning and
> > sanitizing options and build-time debug flags like CONFIG_PAGE_POISONING
> > more coherent. I took the simpler path.
> >
>
> I thought latest work be Vlastimil tried to tackle that. To me, it feels
> like page_poison=on  and init_on_free=1 should bail out and disable one
> of both things. Having both at the same time doesn't sound helpful.

This is exactly how it works, see init_mem_debugging_and_hardening().

Sergei, could you elaborate more on what kind of crash this patch is
trying to fix? Where does it happen and why?