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SubjectRe: [PATCH] mm/page_alloc: fix boot hang in memmap_init_zone
On Tue 13-03-18 23:42:40, 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.

I am sorry to be complaining again, but the code is so obscure that I
would _really_ appreciate some more information about what is going
on here. memblock_next_valid_pfn will most likely return a pfn within
the same memblock and the alignment will move it before the old pfn
which is not valid - so the block has some holes. Is that correct?
If yes then please put it into the changelog. Maybe reuse data provided
by Arnd http://lkml.kernel.org/r/20180314134431.13241-1-ard.biesheuvel@linaro.org

> 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;
> #endif
> continue;
> }
> --
> 2.16.2
>

--
Michal Hocko
SUSE Labs

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