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

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Message-ID: <CA+fCnZdgKpGKGSyY6rmoqzDPTdTOB4DCvQk1NjreUPMRLH3XSQ@mail.gmail.com>
Date:   Tue, 30 Mar 2021 16:48:08 +0200
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     David Hildenbrand <david@...hat.com>,
        Sergei Trofimovich <slyfox@...too.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: page_alloc: ignore init_on_free=1 for page alloc

On Tue, Mar 30, 2021 at 12:07 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 3/30/21 12:00 AM, Andrey Konovalov wrote:
> > On Mon, Mar 29, 2021 at 2:10 PM Vlastimil Babka <vbabka@...e.cz> wrote:
> >>
> >> > commit 855a9c4018f3219db8be7e4b9a65ab22aebfde82
> >> > Author: Andrey Konovalov <andreyknvl@...il.com>
> >> > Date:   Thu Mar 18 17:01:40 2021 +1100
> >> >
> >> >     kasan, mm: integrate page_alloc init with HW_TAGS
> >>
> >> But the mmotm patch/-next commit also changes post_alloc_hook()
> >>
> >> Before the patch it was:
> >> kernel_unpoison_pages(page, 1 << order);
> >> ...
> >> kernel_init_free_pages(page, 1 << order);
> >>
> >> Now it is (for !kasan_has_integrated_init()):
> >>
> >> kernel_init_free_pages(page, 1 << order);
> >>
> >> kernel_unpoison_pages(page, 1 << order);
> >>
> >> That has to be wrong, because we init the page with zeroes and then call
> >> kernel_unpoison_pages() which checks for the 0xaa pattern. Andrey?
> >
> > It's similar to free_pages_prepare(): kernel_unpoison_pages() and
> > want_init_on_alloc() are exclusive, so the order shouldn't matter. Am
> > I missing something?
>
> Yeah, when the allocation has __GFP_ZERO, want_init_on_alloc() will return true
> even with the static branches disabled.

Ah, I see. I'll post a fix soon.

Thank you!