Messages in this thread | | | Date | Fri, 7 Sep 2012 12:47:16 +0900 | From | Yasuaki Ishimatsu <> | Subject | Re: [PATCH v2 3/3] memory-hotplug: bug fix race between isolation and allocation |
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Hi Minchan,
2012/09/07 8:37, Minchan Kim wrote: > Hello Yasuaki, > > On Thu, Sep 06, 2012 at 06:14:39PM +0900, Yasuaki Ishimatsu wrote: >> Hi, Minchan, >> >> 2012/09/06 16:30, Minchan Kim wrote: >>> Hello Yasuaki, >>> >>> On Thu, Sep 06, 2012 at 04:17:54PM +0900, Yasuaki Ishimatsu wrote: >>>> Hi Minchan, >>>> >>>> 2012/09/06 14:16, Minchan Kim wrote: >>>>> Like below, memory-hotplug makes race between page-isolation >>>>> and page-allocation so it can hit BUG_ON in __offline_isolated_pages. >>>>> >>>>> CPU A CPU B >>>>> >>>>> start_isolate_page_range >>>>> set_migratetype_isolate >>>>> spin_lock_irqsave(zone->lock) >>>>> >>>>> free_hot_cold_page(Page A) >>>>> /* without zone->lock */ >>>>> migratetype = get_pageblock_migratetype(Page A); >>>>> /* >>>>> * Page could be moved into MIGRATE_MOVABLE >>>>> * of per_cpu_pages >>>>> */ >>>>> list_add_tail(&page->lru, &pcp->lists[migratetype]); >>>>> >>>>> set_pageblock_isolate >>>>> move_freepages_block >>>>> drain_all_pages >>>>> >>>>> /* Page A could be in MIGRATE_MOVABLE of free_list. */ >>>>> >>>>> check_pages_isolated >>>>> __test_page_isolated_in_pageblock >>>>> /* >>>>> * We can't catch freed page which >>>>> * is free_list[MIGRATE_MOVABLE] >>>>> */ >>>>> if (PageBuddy(page A)) >>>>> pfn += 1 << page_order(page A); >>>>> >>>>> /* So, Page A could be allocated */ >>>>> >>>>> __offline_isolated_pages >>>>> /* >>>>> * BUG_ON hit or offline page >>>>> * which is used by someone >>>>> */ >>>>> BUG_ON(!PageBuddy(page A)); >>>>> >>>>> This patch checks page's migratetype in freelist in __test_page_isolated_in_pageblock. >>>>> So now __test_page_isolated_in_pageblock can check the page caused by above race and >>>>> can fail of memory offlining. >>>>> >>>>> Signed-off-by: Minchan Kim <minchan@kernel.org> >>>>> --- >>>>> mm/page_isolation.c | 5 ++++- >>>>> 1 file changed, 4 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c >>>>> index 87a7929..7ba7405 100644 >>>>> --- a/mm/page_isolation.c >>>>> +++ b/mm/page_isolation.c >>>>> @@ -193,8 +193,11 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn) >>>>> continue; >>>>> } >>>>> page = pfn_to_page(pfn); >>>>> - if (PageBuddy(page)) >>>>> + if (PageBuddy(page)) { >>>>> + if (get_freepage_migratetype(page) != MIGRATE_ISOLATE) >>>>> + break; >>>>> pfn += 1 << page_order(page); >>>>> + } >>>> >>>>> else if (page_count(page) == 0 && >>>>> get_freepage_migratetype(page) == MIGRATE_ISOLATE) >>>> >>>> When do the if statement, the page may be used by someone. >>> >>> I can't understand your point. >>> We already hold zone->lock so that allocator and this function should be atomic >>> when the page is in free_list. >>> If I miss something, could you elaborate it more? >> >> According to your description, the page might be allocated by someone >> at this point. So some value might be set the page->index by the > > It seems you are misunderstanding my point. > Before my patch, Yes. It could be allocated by someone but > after my patch, it couldn't be allocated and inconsistency between > pageblock's migratetype and page's migratetype is detected so that > memory offline would be just failed simply.
Thank you for your explanation. My concern disappeared.
Thanks, Yasuaki Ishimatsu
> >> intended purpose. Thus page->index has the potential to become >> MIGRATE_ISOLATE value. >> >> Thanks, >> Yasuaki Ishimatsu >> >>> >>>> In this case, page->index may have some number. If the number is same as >>>> MIGRATE_ISOLATE, the code goes worng. >>>> >>>> Thanks, >>>> Yasuaki Ishimatsu >>>> >>>>> pfn += 1; >>>>> >>>> >>>> >>>> -- >>>> To unsubscribe, send a message with 'unsubscribe linux-mm' in >>>> the body to majordomo@kvack.org. For more info on Linux MM, >>>> see: http://www.linux-mm.org/ . >>>> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> >>> >> >> >> -- >> To unsubscribe, send a message with 'unsubscribe linux-mm' in >> the body to majordomo@kvack.org. For more info on Linux MM, >> see: http://www.linux-mm.org/ . >> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> >
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