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

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Date:   Tue, 30 Mar 2021 00:07:05 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Andrey Konovalov <andreyknvl@...il.com>
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 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.