linux-kernel - Re: [lkp-robot] [mm, page_alloc] b7ef62aa8a: BUG:kernel_hang_in_boot

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Message-Id: <20170330154026.3ca919cf3b93da81c25724c4@linux-foundation.org>
Date:   Thu, 30 Mar 2017 15:40:26 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     kernel test robot <xiaolong.ye@...el.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Johannes Weiner <hannes@...xchg.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        David Rientjes <rientjes@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...org
Subject: Re: [lkp-robot] [mm, page_alloc] b7ef62aa8a:
 BUG:kernel_hang_in_boot_stage

> > BUG: kernel hang in boot stage
> 
> Thanks, I was able to reproduce and debug this.
> Andrew, please apply the following -fix. There will be conflicts on later
> patches, but with trivial resolution (pages -> free_pages). Thanks!
> 
> ...
>
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1977,6 +1977,9 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
>  		goto single_page;
>  
>  	pages = move_freepages_block(zone, page, start_type);
> +	/* moving whole block can fail due to zone boundary conditions */
> +	if (!pages)
> +		goto single_page;
>  
>  	/* Claim the whole block if over half of it is free */
>  	if (pages >= (1 << (pageblock_order-1)) ||

The result is a bit odd:

	free_pages = move_freepages_block(zone, page, start_type,
						&movable_pages);
	/*
	 * Determine how many pages are compatible with our allocation.
	 * For movable allocation, it's the number of movable pages which
	 * we just obtained. For other types it's a bit more tricky.
	 */
	if (start_type == MIGRATE_MOVABLE) {
		alike_pages = movable_pages;
	} else {
		/*
		 * If we are falling back a RECLAIMABLE or UNMOVABLE allocation
		 * to MOVABLE pageblock, consider all non-movable pages as
		 * compatible. If it's UNMOVABLE falling back to RECLAIMABLE or
		 * vice versa, be conservative since we can't distinguish the
		 * exact migratetype of non-movable pages.
		 */
		if (old_block_type == MIGRATE_MOVABLE)
			alike_pages = pageblock_nr_pages
						- (free_pages + movable_pages);
		else
			alike_pages = 0;
	}

	/* moving whole block can fail due to zone boundary conditions */
	if (!free_pages)
		goto single_page;

should we do `goto single_page' as soon as the move_freepages_block()
call fails?