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Message-ID: <xa1t61jzwfo6.fsf@mina86.com>
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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