(2012/06/11 9:17), Minchan Kim wrote: > d179e84ba fixed the problem[1] in vmscan.c but same problem is here. > Let's fix it. > > [1] http://comments.gmane.org/gmane.linux.kernel.mm/65844 > > I copy and paste d179e84ba's contents for description. > > "It is unsafe to run page_count during the physical pfn scan because > compound_head could trip on a dangling pointer when reading > page->first_page if the compound page is being freed by another CPU." > > Cc: Andrea Arcangeli<aarcange@xxxxxxxxxx> > Cc: Mel Gorman<mgorman@xxxxxxx> > Cc: Michal Hocko<mhocko@xxxxxxx> > Cc: KAMEZAWA Hiroyuki<kamezawa.hiroyu@xxxxxxxxxxxxxx> > Signed-off-by: Minchan Kim<minchan@xxxxxxxxxx> > --- > mm/page_alloc.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 266f267..019c4fe 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5496,7 +5496,11 @@ __count_immobile_pages(struct zone *zone, struct page *page, int count) > continue; > > page = pfn_to_page(check); > - if (!page_count(page)) { > + /* > + * We can't use page_count withou pin a page > + * because another CPU can free compound page. > + */ > + if (!atomic_read(&page->_count)) { > if (PageBuddy(page)) > iter += (1<< page_order(page)) - 1; > continue; Nice Catch. Other than the comment fix already pointed out.. Hmm...BTW, it seems this __count_xxx doesn't have any code for THP/Hugepage.. so, we need more fixes for better code, I think. Hmm, Don't we need !PageTail() check and 'skip thp' code ? Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>