linux-kernel - Re: [BUG] Crash on x86_32 for: mm: page_alloc: avoid merging non-fallbackable pageblocks with others

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Date:   Wed, 30 Mar 2022 16:53:37 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Zi Yan <ziy@...dia.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        David Hildenbrand <david@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [BUG] Crash on x86_32 for: mm: page_alloc: avoid merging
 non-fallbackable pageblocks with others

On Wed, 30 Mar 2022 16:29:28 -0400
Zi Yan <ziy@...dia.com> wrote:

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index bdc8f60ae462..83a90e2973b7 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1108,6 +1108,8 @@ static inline void __free_one_page(struct page *page,
> 
>                 buddy_pfn = __find_buddy_pfn(pfn, order);
>                 buddy = page + (buddy_pfn - pfn);
> +               if (!page_is_buddy(page, buddy, order))
> +                       goto done_merging;
>                 buddy_mt = get_pageblock_migratetype(buddy);
> 
>                 if (migratetype != buddy_mt
> 

The above did not apply to Linus's tree, nor even the problem commit
(before or after), but I found where the code is, and added it manually.

It does appear to allow the machine to boot.

-- Steve