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); _
