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Subject: Re: [mm 4.15-rc8] Random oopses under memory pressure.
To:     Linus Torvalds <torvalds@linux-foundation.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
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Cc:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Tony Luck <tony.luck@intel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Michal Hocko <mhocko@kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        the arch/x86 maintainers <x86@kernel.org>
From:   Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <87aea433-ba6b-8543-d925-3ef36911f124@linux.intel.com>
Date:   Wed, 17 Jan 2018 14:00:54 -0800
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On 01/17/2018 01:39 PM, Linus Torvalds wrote:
> 
> So maybe something like this to test the theory?
> 
>     diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>     index 76c9688b6a0a..f919a5548943 100644
>     --- a/mm/page_alloc.c
>     +++ b/mm/page_alloc.c
>     @@ -756,6 +756,8 @@ static inline void rmv_page_order(struct page *page)
>      static inline int page_is_buddy(struct page *page, struct page *buddy,
>                                                             unsigned int order)
>      {
>     +       if (WARN_ON_ONCE(page_zone(page) != page_zone(buddy)))
>     +               return 0;
>             if (page_is_guard(buddy) && page_order(buddy) == order) {
>                     if (page_zone_id(page) != page_zone_id(buddy))
>                             return 0;

I thought that page_zone_id() stuff was there to prevent this kind of
cross-zone stuff from happening.