From: Michal Hocko <mhocko@kernel.org>
To: Pavel Tatashin <pasha.tatashin@oracle.com>
Cc: steven.sistare@oracle.com, daniel.m.jordan@oracle.com,
akpm@linux-foundation.org, mgorman@techsingularity.net,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 1/1] mm: buddy page accessed before initialized
Date: Thu, 2 Nov 2017 14:32:35 +0100 [thread overview]
Message-ID: <20171102133235.2vfmmut6w4of2y3j@dhcp22.suse.cz> (raw)
In-Reply-To: <20171031155002.21691-2-pasha.tatashin@oracle.com>
On Tue 31-10-17 11:50:02, Pavel Tatashin wrote:
[...]
> The problem happens in this path:
>
> page_alloc_init_late
> deferred_init_memmap
> deferred_init_range
> __def_free
> deferred_free_range
> __free_pages_boot_core(page, order)
> __free_pages()
> __free_pages_ok()
> free_one_page()
> __free_one_page(page, pfn, zone, order, migratetype);
>
> deferred_init_range() initializes one page at a time by calling
> __init_single_page(), once it initializes pageblock_nr_pages pages, it
> calls deferred_free_range() to free the initialized pages to the buddy
> allocator. Eventually, we reach __free_one_page(), where we compute buddy
> page:
> buddy_pfn = __find_buddy_pfn(pfn, order);
> buddy = page + (buddy_pfn - pfn);
>
> buddy_pfn is computed as pfn ^ (1 << order), or pfn + pageblock_nr_pages.
> Thefore, buddy page becomes a page one after the range that currently was
> initialized, and we access this page in this function. Also, later when we
> return back to deferred_init_range(), the buddy page is initialized again.
>
> So, in order to avoid this issue, we must initialize the buddy page prior
> to calling deferred_free_range().
How come we didn't have this problem previously? I am really confused.
> Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.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 97687b38da05..f3ea06db3eed 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1500,9 +1500,17 @@ static unsigned long deferred_init_range(int nid, int zid, unsigned long pfn,
> __init_single_page(page, pfn, zid, nid);
> nr_free++;
> } else {
> - nr_pages += __def_free(&nr_free, &free_base_pfn, &page);
> page = pfn_to_page(pfn);
> __init_single_page(page, pfn, zid, nid);
> + /*
> + * We must free previous range after initializing the
> + * first page of the next range. This is because first
> + * page may be accessed in __free_one_page(), when buddy
> + * page is computed:
> + * buddy_pfn = pfn + pageblock_nr_pages
> + */
> + deferred_free_range(free_base_pfn, nr_free);
> + nr_pages += nr_free;
> free_base_pfn = pfn;
> nr_free = 1;
> cond_resched();
> --
> 2.14.3
>
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2017-11-02 13:32 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-31 15:50 [PATCH v1 0/1] buddy page accessed before initialized Pavel Tatashin
2017-10-31 15:50 ` [PATCH v1 1/1] mm: " Pavel Tatashin
2017-11-02 13:32 ` Michal Hocko [this message]
2017-11-02 13:39 ` Pavel Tatashin
2017-11-02 13:54 ` Michal Hocko
2017-11-02 14:00 ` Pavel Tatashin
2017-11-02 14:08 ` Michal Hocko
2017-11-02 14:16 ` Pavel Tatashin
2017-11-02 14:27 ` Michal Hocko
2017-11-02 16:10 ` Pavel Tatashin
2017-11-03 8:59 ` Michal Hocko
2017-11-03 14:17 ` Pavel Tatashin
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