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Date:	Tue, 17 Jun 2014 20:32:09 +0200
From:	Michal Nazarewicz <mina86@...a86.com>
To:	David Rientjes <rientjes@...gle.com>,
	Mark Salter <msalter@...hat.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: fix MAX_ORDER for 64K pagesize

On Wed, Jun 11 2014, David Rientjes wrote:
> On Wed, 11 Jun 2014, Mark Salter wrote:
>
>> With a kernel configured with ARM64_64K_PAGES && !TRANSPARENT_HUGEPAGE
>> I get this at early boot:
>> 
>>   SMP: Total of 8 processors activated.
>>   devtmpfs: initialized
>>   Unable to handle kernel NULL pointer dereference at virtual address 00000008
>>   pgd = fffffe0000050000
>>   [00000008] *pgd=00000043fba00003, *pmd=00000043fba00003, *pte=00e0000078010407
>>   Internal error: Oops: 96000006 [#1] SMP
>>   Modules linked in:
>>   CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.15.0-rc864k+ #44
>>   task: fffffe03bc040000 ti: fffffe03bc080000 task.ti: fffffe03bc080000
>>   PC is at __list_add+0x10/0xd4
>>   LR is at free_one_page+0x270/0x638
>>   ...
>>   Call trace:
>>   [<fffffe00003ee970>] __list_add+0x10/0xd4
>>   [<fffffe000019c478>] free_one_page+0x26c/0x638
>>   [<fffffe000019c8c8>] __free_pages_ok.part.52+0x84/0xbc
>>   [<fffffe000019d5e8>] __free_pages+0x74/0xbc
>>   [<fffffe0000c01350>] init_cma_reserved_pageblock+0xe8/0x104
>>   [<fffffe0000c24de0>] cma_init_reserved_areas+0x190/0x1e4
>>   [<fffffe0000090418>] do_one_initcall+0xc4/0x154
>>   [<fffffe0000bf0a50>] kernel_init_freeable+0x204/0x2a8
>>   [<fffffe00007520a0>] kernel_init+0xc/0xd4
>> 
>> This happens in this configuration because __free_one_page() is called
>> with an order greater than MAX_ORDER, accesses past zone->free_list[]
>> and passes a bogus list_head to list_add().
>> 
>> arch/arm64/Kconfig has:
>> 
>>   config FORCE_MAX_ZONEORDER
>> 	int
>> 	default "14" if (ARM64_64K_PAGES && TRANSPARENT_HUGEPAGE)
>> 	default "11"
>> 
>> So with THP turned off MAX_ORDER == 11 but init_cma_reserved_pageblock()
>> passes __free_pages() an order of pageblock_order which is based on
>> (HPAGE_SHIFT - PAGE_SHIFT) which is 13 for 64K pages. I worked around
>> this by removing the THP test so FORCE_MAX_ZONEORDER is always 14 for
>> ARM64_64K_PAGES.
>> 
>> Signed-off-by: Mark Salter <msalter@...hat.com>
>> ---
>>  arch/arm64/Kconfig | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index 7295419..42a334e 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -269,7 +269,7 @@ config XEN
>>  
>>  config FORCE_MAX_ZONEORDER
>>  	int
>> -	default "14" if (ARM64_64K_PAGES && TRANSPARENT_HUGEPAGE)
>> +	default "14" if ARM64_64K_PAGES
>>  	default "11"
>>  
>>  endmenu
>
> Any reason to not switch this to
>
> 	ARM64_64K_PAGES && TRANSPARENT_HUGEPAGE && CMA
>
> instead?  If pageblock_order > MAX_ORDER because of 
> HPAGE_SHIFT > PAGE_SHIFT, then cma is always going to be passing a 
> too-large-order to free_pages_prepare() via this path.
>
> Adding Michal and Marek to the cc.

The correct fix would be to change init_cma_reserved_pageblock such that
it checks whether pageblock_order > MAX_ORDER and if so frees each max
order page of the pageblock individually:

--------- >8 ---------------------------------------------------------
From: Michal Nazarewicz <mina86@...a86.com>
Subject: [PATCH] mm: cma: fix cases where pageblock is bigger then MAX_ORDER

With a kernel configured with ARM64_64K_PAGES && !TRANSPARENT_HUGEPAGE,
the following is triggered at early boot:

  SMP: Total of 8 processors activated.
  devtmpfs: initialized
  Unable to handle kernel NULL pointer dereference at virtual address 00000008
  pgd = fffffe0000050000
  [00000008] *pgd=00000043fba00003, *pmd=00000043fba00003, *pte=00e0000078010407
  Internal error: Oops: 96000006 [#1] SMP
  Modules linked in:
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.15.0-rc864k+ #44
  task: fffffe03bc040000 ti: fffffe03bc080000 task.ti: fffffe03bc080000
  PC is at __list_add+0x10/0xd4
  LR is at free_one_page+0x270/0x638
  ...
  Call trace:
  [<fffffe00003ee970>] __list_add+0x10/0xd4
  [<fffffe000019c478>] free_one_page+0x26c/0x638
  [<fffffe000019c8c8>] __free_pages_ok.part.52+0x84/0xbc
  [<fffffe000019d5e8>] __free_pages+0x74/0xbc
  [<fffffe0000c01350>] init_cma_reserved_pageblock+0xe8/0x104
  [<fffffe0000c24de0>] cma_init_reserved_areas+0x190/0x1e4
  [<fffffe0000090418>] do_one_initcall+0xc4/0x154
  [<fffffe0000bf0a50>] kernel_init_freeable+0x204/0x2a8
  [<fffffe00007520a0>] kernel_init+0xc/0xd4

This happens in this configuration because __free_one_page() is called
with an order greater than MAX_ORDER, accesses past zone->free_list[]
and passes a bogus list_head to list_add().

arch/arm64/Kconfig has:

  config FORCE_MAX_ZONEORDER
	int
	default "14" if (ARM64_64K_PAGES && TRANSPARENT_HUGEPAGE)
	default "11"

So with THP turned off MAX_ORDER == 11 but init_cma_reserved_pageblock()
passes __free_pages() an order of pageblock_order which is based on
(HPAGE_SHIFT - PAGE_SHIFT) which is 13 for 64K pages.

Fix the problem by changing init_cma_reserved_pageblock() such that it
splits pageblock into individual MAX_ORDER pages if pageblock is
bigger than a MAX_ORDER page.

Signed-off-by: Michal Nazarewicz <mina86@...a86.com>
Reported-by: Mark Salter <msalter@...hat.com>
---
 mm/page_alloc.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5dba293..6e657ce 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -801,7 +801,15 @@ void __init init_cma_reserved_pageblock(struct page *page)
 
 	set_page_refcounted(page);
 	set_pageblock_migratetype(page, MIGRATE_CMA);
-	__free_pages(page, pageblock_order);
+	if (pageblock_order > MAX_ORDER) {
+		struct page *subpage = p;
+		unsigned count = 1 << (pageblock_order - MAX_ORDER);
+		do {
+			__free_pages(subpage, pageblock_order);
+		} while (subpage += MAX_ORDER_NR_PAGES, --count);
+	} else {
+		__free_pages(page, pageblock_order);
+	}
 	adjust_managed_page_count(page, pageblock_nr_pages);
 }
 #endif
--------- >8 ---------------------------------------------------------

Thoughts?  This has not been tested and I think it may cause performance
degradation in some cases since pageblock_order is not always
a constant, so the comparison may end up not being stripped away even on
systems where it's always false.

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +--<mpn@...gle.com>--<xmpp:mina86@...ber.org>--ooO--(_)--Ooo--
--
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