Re: [PATCH v6 1/2] mm: migration: fix migration of huge PMD shared pages

On Thu 23-08-18 13:59:16, Mike Kravetz wrote: [...]

@@ -1409,6 +1419,32 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, subpage = page - page_to_pfn(page) + pte_pfn(*pvmw.pte); address = pvmw.address;

• if (PageHuge(page)) {
  

• 	if (huge_pmd_unshare(mm, &address, pvmw.pte)) {
  

• 		/*
  

• 		 * huge_pmd_unshare unmapped an entire PMD
  

• 		 * page.  There is no way of knowing exactly
  

• 		 * which PMDs may be cached for this mm, so
  

• 		 * we must flush them all.  start/end were
  

• 		 * already adjusted above to cover this range.
  

• 		 */
  

• 		flush_cache_range(vma, start, end);
  

• 		flush_tlb_range(vma, start, end);
  

• 		mmu_notifier_invalidate_range(mm, start, end);
  

• 		/*
  

• 		 * The ref count of the PMD page was dropped
  

• 		 * which is part of the way map counting
  

• 		 * is done for shared PMDs.  Return 'true'
  

• 		 * here.  When there is no other sharing,
  

• 		 * huge_pmd_unshare returns false and we will
  

• 		 * unmap the actual page and drop map count
  

• 		 * to zero.
  

• 		 */
  

• 		page_vma_mapped_walk_done(&pvmw);
  

• 		break;
  

• 	}
  

• }
  

Wait a second. This is not correct, right? You have to call the notifiers after page_vma_mapped_walk_done because they might be sleepable and we are still holding the pte lock. This is btw. a problem for other users of mmu_notifier_invalidate_range in try_to_unmap_one, unless I am terribly confused. This would suggest 369ea8242c0fb is incorrect.