On Thu 23-08-18 15:06:08, James Morse wrote: [...] > My best-guess is that pfn_valid_within() shouldn't be optimised out if > ARCH_HAS_HOLES_MEMORYMODEL, even if HOLES_IN_ZONE isn't set. > > Does something like this solve the problem?: > ============================%<============================ > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 32699b2dc52a..5e27095a15f4 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -1295,7 +1295,7 @@ void memory_present(int nid, unsigned long start, unsigned > long end); > * pfn_valid_within() should be used in this case; we optimise this away > * when we have no holes within a MAX_ORDER_NR_PAGES block. > */ > -#ifdef CONFIG_HOLES_IN_ZONE > +#if defined(CONFIG_HOLES_IN_ZONE) || defined(CONFIG_ARCH_HAS_HOLES_MEMORYMODEL) > #define pfn_valid_within(pfn) pfn_valid(pfn) > #else > #define pfn_valid_within(pfn) (1) > ============================%<============================ This is the first time I hear about CONFIG_ARCH_HAS_HOLES_MEMORYMODEL. Why it doesn't imply CONFIG_HOLES_IN_ZONE? > > I analyzed the assembler: > > PageBuddy in move_freepages returns false > > Then we call PageLRU, the macro calls PF_HEAD which is compound_page() > > compound_page reads page->compound_head, it is 0xffffffffffffffff, so it > > resturns 0xfffffffffffffffe - and accessing this address causes crash > > Thanks! > That wasn't straightforward to work out without the vmlinux. > > Because you see all-ones, even in KVM, it looks like the struct page is being > initialized like that deliberately... I haven't found where this might be happening. It should be sparse_add_one_section #ifdef CONFIG_DEBUG_VM /* * Poison uninitialized struct pages in order to catch invalid flags * combinations. */ memset(memmap, PAGE_POISON_PATTERN, sizeof(struct page) * PAGES_PER_SECTION); #endif -- Michal Hocko SUSE Labs
