Date:   Tue, 4 Apr 2017 14:45:08 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Tobias Regnery <tobias.regnery@...il.com>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
        Tang Chen <tangchen@...fujitsu.com>, qiuxishi@...wei.com,
        Kani Toshimitsu <toshi.kani@....com>, slaoub@...il.com,
        Joonsoo Kim <js1304@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Zhang Zhen <zhenzhang.zhang@...wei.com>,
        David Rientjes <rientjes@...gle.com>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Dan Williams <dan.j.williams@...il.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Lai Jiangshan <laijs@...fujitsu.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH 5/6] mm, memory_hotplug: do not associate hotadded memory
 to zones until online

On Tue 04-04-17 14:21:19, Tobias Regnery wrote:
[...]
> Hi Michal,

Hi

> building an x86 allmodconfig with next-20170404 results in the following 
> section mismatch warnings probably caused by this patch:
> 
> WARNING: mm/built-in.o(.text+0x5a1c2): Section mismatch in reference from the function move_pfn_range_to_zone() to the function .meminit.text:memmap_init_zone()
> The function move_pfn_range_to_zone() references
> the function __meminit memmap_init_zone().
> This is often because move_pfn_range_to_zone lacks a __meminit 
> annotation or the annotation of memmap_init_zone is wrong.

Right. __add_pages which used to call memmap_init_zone before
is __ref (to hide it the checker) which is not the case for
move_pfn_range_to_zone. I cannot say I would see the point of separating
all meminit functions because they are not going away but using __ref
for move_pfn_range_to_zone should be as safe as __add_pages is.

> WARNING: mm/built-in.o(.text+0x5a25b): Section mismatch in reference from the function move_pfn_range_to_zone() to the function .meminit.text:init_currently_empty_zone()
> The function move_pfn_range_to_zone() references
> the function __meminit init_currently_empty_zone().
> This is often because move_pfn_range_to_zone lacks a __meminit 
> annotation or the annotation of init_currently_empty_zone is wrong.

and this is the same thing. Thanks a lot. The following patch should fix
it. I will keep it separate to have a reference why this has been
done...
---
>From 1ff2996125393601a28065c44d790145078483db Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@...e.com>
Date: Tue, 4 Apr 2017 14:36:25 +0200
Subject: [PATCH] mm, hotplug: fix the section mismatch warning

Tobias has reported following section mismatches introduced by "mm,
memory_hotplug: do not associate hotadded memory to zones until online".

WARNING: mm/built-in.o(.text+0x5a1c2): Section mismatch in reference from the function move_pfn_range_to_zone() to the function .meminit.text:memmap_init_zone()
The function move_pfn_range_to_zone() references
the function __meminit memmap_init_zone().
This is often because move_pfn_range_to_zone lacks a __meminit
annotation or the annotation of memmap_init_zone is wrong.

WARNING: mm/built-in.o(.text+0x5a25b): Section mismatch in reference from the function move_pfn_range_to_zone() to the function .meminit.text:init_currently_empty_zone()
The function move_pfn_range_to_zone() references
the function __meminit init_currently_empty_zone().
This is often because move_pfn_range_to_zone lacks a __meminit
annotation or the annotation of init_currently_empty_zone is wrong.

WARNING: vmlinux.o(.text+0x188aa2): Section mismatch in reference from the function move_pfn_range_to_zone() to the function .meminit.text:memmap_init_zone()
The function move_pfn_range_to_zone() references
the function __meminit memmap_init_zone().
This is often because move_pfn_range_to_zone lacks a __meminit
annotation or the annotation of memmap_init_zone is wrong.

WARNING: vmlinux.o(.text+0x188b3b): Section mismatch in reference from the function move_pfn_range_to_zone() to the function .meminit.text:init_currently_empty_zone()
The function move_pfn_range_to_zone() references
the function __meminit init_currently_empty_zone().
This is often because move_pfn_range_to_zone lacks a __meminit
annotation or the annotation of init_currently_empty_zone is wrong.

Both memmap_init_zone and init_currently_empty_zone are marked __meminit
but move_pfn_range_to_zone is used outside of __meminit sections (e.g.
devm_memremap_pages) so we have to hide it from the checker by __ref
annotation.

Reported-by: Tobias Regnery <tobias.regnery@...il.com>
Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 mm/memory_hotplug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 0e21b9f67c9d..a358d7a67651 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -884,7 +884,7 @@ static void __meminit resize_pgdat_range(struct pglist_data *pgdat, unsigned lon
 	pgdat->node_spanned_pages = max(start_pfn + nr_pages, old_end_pfn) - pgdat->node_start_pfn;
 }
 
-void move_pfn_range_to_zone(struct zone *zone,
+void __ref move_pfn_range_to_zone(struct zone *zone,
 		unsigned long start_pfn, unsigned long nr_pages)
 {
 	struct pglist_data *pgdat = zone->zone_pgdat;
-- 
2.11.0

-- 
Michal Hocko
SUSE Labs

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