linux-kernel - Re: [v6 02/15] x86/mm: setting fields in deferred pages

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Message-ID: <20170814114326.GH19063@dhcp22.suse.cz>
Date:   Mon, 14 Aug 2017 13:43:26 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Pasha Tatashin <pasha.tatashin@...cle.com>
Cc:     linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        x86@...nel.org, kasan-dev@...glegroups.com, borntraeger@...ibm.com,
        heiko.carstens@...ibm.com, davem@...emloft.net,
        willy@...radead.org, ard.biesheuvel@...aro.org,
        will.deacon@....com, catalin.marinas@....com, sam@...nborg.org
Subject: Re: [v6 02/15] x86/mm: setting fields in deferred pages

On Fri 11-08-17 11:39:41, Pasha Tatashin wrote:
> >AFAIU register_page_bootmem_info_node is only about struct pages backing
> >pgdat, usemap and memmap. Those should be in reserved memblocks and we
> >do not initialize those at later times, they are not relevant to the
> >deferred initialization as your changelog suggests so the ordering with
> >get_page_bootmem shouldn't matter. Or am I missing something here?
> 
> The pages for pgdata, usemap, and memmap are part of reserved, and thus
> getting initialized when free_all_bootmem() is called.
> 
> So, we have something like this in mem_init()
> 
> register_page_bootmem_info
>  register_page_bootmem_info_node
>   get_page_bootmem
>    .. setting fields here ..
>    such as: page->freelist = (void *)type;
> 
> free_all_bootmem()
>  free_low_memory_core_early()
>   for_each_reserved_mem_region()
>    reserve_bootmem_region()
>     init_reserved_page() <- Only if this is deferred reserved page
>      __init_single_pfn()
>       __init_single_page()
>           memset(0) <-- Loose the set fields here!

OK, I have missed that part. Please make it explicit in the changelog.
It is quite easy to get lost in the deep call chains.
-- 
Michal Hocko
SUSE Labs