Re: [PATCH] mm/page_alloc: fix boot hang in memmap_init_zone

[Jia He <hejianet@gmail.com>]

Hi Daniel


On 3/14/2018 6:42 AM, Daniel Vacek Wrote:
> On some architectures (reported on arm64) commit 864b75f9d6b01 ("mm/page_alloc: fix memmap_init_zone pageblock alignment")
> causes a boot hang. This patch fixes the hang making sure the alignment
> never steps back.
>
> Link: http://lkml.kernel.org/r/0485727b2e82da7efbce5f6ba42524b429d0391a.1520011945.git.neelx@redhat.com
> Fixes: 864b75f9d6b01 ("mm/page_alloc: fix memmap_init_zone pageblock alignment")
> Signed-off-by: Daniel Vacek <neelx@redhat.com>
> Tested-by: Sudeep Holla <sudeep.holla@arm.com>
> Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Paul Burton <paul.burton@imgtec.com>
> Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: <stable@vger.kernel.org>
> ---
>   mm/page_alloc.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3d974cb2a1a1..e033a6895c6f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5364,9 +5364,14 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
>   			 * is not. move_freepages_block() can shift ahead of
>   			 * the valid region but still depends on correct page
>   			 * metadata.
> +			 * Also make sure we never step back.
>   			 */
> -			pfn = (memblock_next_valid_pfn(pfn, end_pfn) &
> +			unsigned long next_pfn;
> +
> +			next_pfn = (memblock_next_valid_pfn(pfn, end_pfn) &
>   					~(pageblock_nr_pages-1)) - 1;
> +			if (next_pfn > pfn)
> +				pfn = next_pfn;
It didn't resolve the booting hang issue in my arm64 server.
what if memblock_next_valid_pfn(pfn, end_pfn) is 32 and 
pageblock_nr_pages is 8196?
Thus, next_pfn will be (unsigned long)-1 and be larger than pfn.
So still there is an infinite loop here.

Cheers,
Jia He
>   #endif
>   			continue;
>   		}

-- 
Cheers,
Jia