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Message-ID: <1403557803.755.53.camel@deneb.redhat.com>
Date: Mon, 23 Jun 2014 17:10:03 -0400
From: Mark Salter <msalter@...hat.com>
To: Michal Nazarewicz <mina86@...a86.com>
Cc: David Rientjes <rientjes@...gle.com>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Catalin Marinas <catalin.marinas@....com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3] mm: page_alloc: fix CMA area initialisation when
pageblock > MAX_ORDER
On Mon, 2014-06-23 at 21:40 +0200, Michal Nazarewicz wrote:
> 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 because init_cma_reserved_pageblock() calls
> __free_one_page() with pageblock_order as page order but it is bigger
> han MAX_ORDER. This in turn causes accesses past zone->free_list[].
>
> 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.
>
> In cases where !CONFIG_HUGETLB_PAGE_SIZE_VARIABLE, which is all
> architectures expect for ia64, powerpc and tile at the moment, the
> “pageblock_order > MAX_ORDER” condition will be optimised out since
> both sides of the operator are constants. In cases where pageblock
> size is variable, the performance degradation should not be
> significant anyway since init_cma_reserved_pageblock() is called
> only at boot time at most MAX_CMA_AREAS times which by default is
> eight.
>
> Cc: stable@...r.kernel.org
> Signed-off-by: Michal Nazarewicz <mina86@...a86.com>
> Reported-by: Mark Salter <msalter@...hat.com>
> Tested-by: Christopher Covington <cov@...eaurora.org>
> ---
> mm/page_alloc.c | 16 ++++++++++++++--
> 1 file changed, 14 insertions(+), 2 deletions(-)
>
> Mark Salter wrote:
> > I ended up needing this (on top of your patch) to get the system to
> > boot. Each MAX_ORDER-1 group needs the refcount and migratetype set
> > so that __free_pages does the right thing.
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 02fb1ed..a7ca6cc 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -799,17 +799,18 @@ void __init init_cma_reserved_pageblock(struct page *page)
> > set_page_count(p, 0);
> > } while (++p, --i);
> >
> > - set_page_refcounted(page);
> > - set_pageblock_migratetype(page, MIGRATE_CMA);
> > -
> > - if (pageblock_order > MAX_ORDER) {
> > - i = pageblock_order - MAX_ORDER;
> > + if (pageblock_order >= MAX_ORDER) {
> > + i = pageblock_order - MAX_ORDER + 1;
> > i = 1 << i;
> > p = page;
> > do {
> > - __free_pages(p, MAX_ORDER);
> > + set_page_refcounted(p);
> > + set_pageblock_migratetype(p, MIGRATE_CMA);
> > + __free_pages(p, MAX_ORDER - 1);
> > } while (p += MAX_ORDER_NR_PAGES, --i);
> > } else {
> > + set_page_refcounted(page);
> > + set_pageblock_migratetype(page, MIGRATE_CMA);
> > __free_pages(page, pageblock_order);
> > }
>
> This is kinda embarrassing, dunno how I missed that.
>
> But each page actually does not need to have migratetype set, does it?
> All of those pages are in a single pageblock so a single call
> suffices. If you track set_pageblock_migratetype down to pfn_to_bitidx
> there is:
>
> return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS;
>
> so for pfns inside of a pageblock, they get truncated. Or did I miss
> yet another thing?
Nope, my turn to miss something. You only need to set migrate type
once per pageblock.
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index ee92384..fef9614 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -816,9 +816,21 @@ void __init init_cma_reserved_pageblock(struct page *page)
> set_page_count(p, 0);
> } while (++p, --i);
>
> - set_page_refcounted(page);
> set_pageblock_migratetype(page, MIGRATE_CMA);
> - __free_pages(page, pageblock_order);
> +
> + if (pageblock_order >= MAX_ORDER) {
> + i = pageblock_nr_pages;
> + p = page;
> + do {
> + set_page_refcounted(p);
> + __free_pages(p, MAX_ORDER - 1);
> + p += MAX_ORDER_NR_PAGES;
> + } while (i -= MAX_ORDER_NR_PAGES);
> + } else {
> + set_page_refcounted(page);
> + __free_pages(page, pageblock_order);
> + }
> +
> adjust_managed_page_count(page, pageblock_nr_pages);
> }
> #endif
This version works for me. Thanks.
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