On 27.09.19 23:59, Andrew Morton wrote: > On Fri, 27 Sep 2019 17:28:06 -0400 Qian Cai <cai@xxxxxx> wrote: > >>> >>> So I think you've moved the arch_free_page() to be after the final >>> thing which can access page contents, yes? If so, we should have a >>> comment in free_pages_prepare() to attmept to prevent this problem from >>> reoccurring as the code evolves? >> >> Right, something like this above arch_free_page() there? >> >> /* >> * It needs to be just above kernel_map_pages(), as s390 could mark those >> * pages unused and then trigger a fault when accessing. >> */ > > I did this. > > --- a/mm/page_alloc.c~mm-page_alloc-fix-a-crash-in-free_pages_prepare-fix > +++ a/mm/page_alloc.c > @@ -1179,7 +1179,13 @@ static __always_inline bool free_pages_p > kernel_init_free_pages(page, 1 << order); > > kernel_poison_pages(page, 1 << order, 0); > + /* > + * arch_free_page() can make the page's contents inaccessible. s390 > + * does this. So nothing which can access the page's contents should > + * happen after this. > + */ > arch_free_page(page, order); > + > if (debug_pagealloc_enabled()) > kernel_map_pages(page, 1 << order, 0); With that Acked-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
