Messages in this thread | | | Date | Thu, 6 Sep 2012 18:14:39 +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,
2012/09/06 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 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> >
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