On Fri, Jul 27, 2012 at 07:22:48PM +0900, Kamezawa Hiroyuki wrote:
> (2012/07/23 9:48), 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));
> >
> > Signed-off-by: Minchan Kim <minc...@kernel.org>
>
> Ah, hm. Then, you say the page in MIGRATE_MOVABLE will not be isolated
> and may be used again.
Yes.
>
>
> > ---
> > I found this problem during code review so please confirm it.
> > Kame?
> >
> > 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 acf65a7..4699d1f 100644
> > --- a/mm/page_isolation.c
> > +++ b/mm/page_isolation.c
> > @@ -196,8 +196,11 @@ __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_page_migratetype(page) != MIGRATE_ISOLATE)
> > + break;
>
> Doesn't this work enough ? The problem is MIGRATE_TYPE and list_head
> mis-match.
I guess you are confused between get_page_migratetype and
get_pageblock_migratetype.
It's not get_pageblock_migratetype but get_page_migratetype which is introduced
for detecting
MIGRATE_TYPE and list_head mismatch in [1,2/3].
>
> Thanks,
> -Kame
>
>
>
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