linux-kernel - Re: [PATCH] mm: deferred_init

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Message-Id: <071d574f-1d8c-5be9-ec92-6227db01bbd3@linux.vnet.ibm.com>
Date:   Fri, 6 Oct 2017 12:18:31 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>,
        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, mhocko@...nel.org, ard.biesheuvel@...aro.org,
        mark.rutland@....com, will.deacon@....com, catalin.marinas@....com,
        sam@...nborg.org, mgorman@...hsingularity.net,
        steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        bob.picco@...cle.com
Subject: Re: [PATCH] mm: deferred_init_memmap improvements

On 10/04/2017 08:59 PM, Pavel Tatashin wrote:
> This patch fixes another existing issue on systems that have holes in
> zones i.e CONFIG_HOLES_IN_ZONE is defined.
> 
> In for_each_mem_pfn_range() we have code like this:
> 
> if (!pfn_valid_within(pfn)
> 	goto free_range;
> 
> Note: 'page' is not set to NULL and is not incremented but 'pfn' advances.

page is initialized to NULL at the beginning of the function.
PFN advances but we dont proceed unless pfn_valid_within(pfn)
holds true which basically should have checked with arch call
back if the PFN is valid in presence of memory holes as well.
Is not this correct ?

> Thus means if deferred struct pages are enabled on systems with these kind
> of holes, linux would get memory corruptions. I have fixed this issue by
> defining a new macro that performs all the necessary operations when we
> free the current set of pages.

If we bail out in case PFN is not valid, then how corruption
can happen ?