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SubjectRe: [PATCH v1 1/2] mm/page_alloc: fix and rework pfn handling in memmap_init_zone()
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> Am 03.02.2020 um 22:35 schrieb Alexander Duyck <alexander.duyck@gmail.com>:
>
> On Mon, Jan 13, 2020 at 6:40 AM David Hildenbrand <david@redhat.com> wrote:
>>
>> Let's update the pfn manually whenever we continue the loop. This makes
>> the code easier to read but also less error prone (and we can directly
>> fix one issue).
>>
>> When overlap_memmap_init() returns true, pfn is updated to
>> "memblock_region_memory_end_pfn(r)". So it already points at the *next*
>> pfn to process. Incrementing the pfn another time is wrong, we might
>> leave one uninitialized. I spotted this by inspecting the code, so I have
>> no idea if this is relevant in practise (with kernelcore=mirror).
>>
>> Fixes: a9a9e77fbf27 ("mm: move mirrored memory specific code outside of memmap_init_zone")
>> Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Michal Hocko <mhocko@kernel.org>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Cc: Kirill A. Shutemov <kirill@shutemov.name>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>> mm/page_alloc.c | 9 ++++++---
>> 1 file changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index a41bd7341de1..a92791512077 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -5905,18 +5905,20 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
>> }
>> #endif
>>
>> - for (pfn = start_pfn; pfn < end_pfn; pfn++) {
>> + for (pfn = start_pfn; pfn < end_pfn; ) {
>> /*
>> * There can be holes in boot-time mem_map[]s handed to this
>> * function. They do not exist on hotplugged memory.
>> */
>> if (context == MEMMAP_EARLY) {
>> if (!early_pfn_valid(pfn)) {
>> - pfn = next_pfn(pfn) - 1;
>> + pfn = next_pfn(pfn);
>> continue;
>> }
>> - if (!early_pfn_in_nid(pfn, nid))
>> + if (!early_pfn_in_nid(pfn, nid)) {
>> + pfn++;
>> continue;
>> + }
>> if (overlap_memmap_init(zone, &pfn))
>> continue;
>> if (defer_init(nid, pfn, end_pfn))
>
> I'm pretty sure this is a bit broken. The overlap_memmap_init is going
> to return memblock_region_memory_end_pfn instead of the start of the
> next region. I think that is going to stick you in a mirrored region
> without advancing in that case. You would also need to have that case
> do a pfn++ before the continue;

Thanks for having a look.

Did you read the description regarding this change?
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