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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-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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