Re: [BUG] 3.2.2 crash in isolate_migratepages

["Michal Nazarewicz" <mina86@mina86.com>]

> On 1/30/12 1:09 AM, Mel Gorman wrote:
>> The migrate_pfn is just below a memory hole and the free scanner is
>> beyond the hole. When isolate_migratepages started, it scans from
>> migrate_pfn to migrate_pfn+pageblock_nr_pages which is now in a memory
>> hole. It checks pfn_valid() on the first PFN but then scans into the
>> hole where there are not necessarily valid struct pages.
>>
>> This patch ensures that isolate_migratepages calls pfn_valid when
>> necessary.
>>
>> Signed-off-by: Mel Gorman <mgorman@suse.de>

If anyone cares, this looks good to me, so:

Acked-by: Michal Nazarewicz <mina86@mina86.com>

>> ---
>>  mm/compaction.c |   13 +++++++++++++
>>  1 files changed, 13 insertions(+), 0 deletions(-)
>>
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index 899d956..edc1e26 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -313,6 +313,19 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
>>  		} else if (!locked)
>>  			spin_lock_irq(&zone->lru_lock);
>>
>> +		/*
>> +		 * migrate_pfn does not necessarily start aligned to a
>> +		 * pageblock. Ensure that pfn_valid is called when moving
>> +		 * into a new MAX_ORDER_NR_PAGES range in case of large
>> +		 * memory holes within the zone
>> +		 */
>> +		if ((low_pfn & (MAX_ORDER_NR_PAGES - 1)) == 0) {
>> +			if (!pfn_valid(low_pfn)) {
>> +				low_pfn += MAX_ORDER_NR_PAGES - 1;
>> +				continue;
>> +			}
>> +		}
>> +
>>  		if (!pfn_valid_within(low_pfn))
>>  			continue;
>>  		nr_scanned++;

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +----<email/xmpp: mpn@google.com>--------------ooO--(_)--Ooo--

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