1 files changed, 62 insertions, 29 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b113515..b545590 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2374,6 +2374,34 @@ static bool hugepage_vma_check(struct vm_area_struct *vma)
 }
 
 /*
+ * If mmap_sem temporarily dropped, revalidate vma
+ * before taking mmap_sem.
+ * Return 0 if succeeds, otherwise return none-zero
+ * value (scan code).
+ */
+
+static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address)
+{
+	struct vm_area_struct *vma;
+	unsigned long hstart, hend;
+
+	if (unlikely(khugepaged_test_exit(mm)))
+		return SCAN_ANY_PROCESS;
+
+	vma = find_vma(mm, address);
+	if (!vma)
+		return SCAN_VMA_NULL;
+
+	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
+	hend = vma->vm_end & HPAGE_PMD_MASK;
+	if (address < hstart || address + HPAGE_PMD_SIZE > hend)
+		return SCAN_ADDRESS_RANGE;
+	if (!hugepage_vma_check(vma))
+		return SCAN_VMA_CHECK;
+	return 0;
+}
+
+/*
  * Bring missing pages in from swap, to complete THP collapse.
  * Only done if khugepaged_scan_pmd believes it is worthwhile.
  *
@@ -2381,7 +2409,7 @@ static bool hugepage_vma_check(struct vm_area_struct *vma)
  * but with mmap_sem held to protect against vma changes.
  */
 
-static void __collapse_huge_page_swapin(struct mm_struct *mm,
+static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 					struct vm_area_struct *vma,
 					unsigned long address, pmd_t *pmd)
 {
@@ -2397,11 +2425,18 @@ static void __collapse_huge_page_swapin(struct mm_struct *mm,
 			continue;
 		swapped_in++;
 		ret = do_swap_page(mm, vma, _address, pte, pmd,
-				   FAULT_FLAG_ALLOW_RETRY|FAULT_FLAG_RETRY_NOWAIT,
+				   FAULT_FLAG_ALLOW_RETRY,
 				   pteval);
+		/* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */
+		if (ret & VM_FAULT_RETRY) {
+			down_read(&mm->mmap_sem);
+			/* vma is no longer available, don't continue to swapin */
+			if (hugepage_vma_revalidate(mm, address))
+				return false;
+		}
 		if (ret & VM_FAULT_ERROR) {
 			trace_mm_collapse_huge_page_swapin(mm, swapped_in, 0);
-			return;
+			return false;
 		}
 		/* pte is unmapped now, we need to map it */
 		pte = pte_offset_map(pmd, _address);
@@ -2409,6 +2444,7 @@ static void __collapse_huge_page_swapin(struct mm_struct *mm,
 	pte--;
 	pte_unmap(pte);
 	trace_mm_collapse_huge_page_swapin(mm, swapped_in, 1);
+	return true;
 }
 
 static void collapse_huge_page(struct mm_struct *mm,
@@ -2423,7 +2459,6 @@ static void collapse_huge_page(struct mm_struct *mm,
 	struct page *new_page;
 	spinlock_t *pmd_ptl, *pte_ptl;
 	int isolated = 0, result = 0;
-	unsigned long hstart, hend;
 	struct mem_cgroup *memcg;
 	unsigned long mmun_start;	/* For mmu_notifiers */
 	unsigned long mmun_end;		/* For mmu_notifiers */
@@ -2446,39 +2481,37 @@ static void collapse_huge_page(struct mm_struct *mm,
 		goto out_nolock;
 	}
 
-	/*
-	 * Prevent all access to pagetables with the exception of
-	 * gup_fast later hanlded by the ptep_clear_flush and the VM
-	 * handled by the anon_vma lock + PG_lock.
-	 */
-	down_write(&mm->mmap_sem);
-	if (unlikely(khugepaged_test_exit(mm))) {
-		result = SCAN_ANY_PROCESS;
+	down_read(&mm->mmap_sem);
+	result = hugepage_vma_revalidate(mm, address);
+	if (result)
 		goto out;
-	}
 
-	vma = find_vma(mm, address);
-	if (!vma) {
-		result = SCAN_VMA_NULL;
-		goto out;
-	}
-	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
-	hend = vma->vm_end & HPAGE_PMD_MASK;
-	if (address < hstart || address + HPAGE_PMD_SIZE > hend) {
-		result = SCAN_ADDRESS_RANGE;
-		goto out;
-	}
-	if (!hugepage_vma_check(vma)) {
-		result = SCAN_VMA_CHECK;
-		goto out;
-	}
 	pmd = mm_find_pmd(mm, address);
 	if (!pmd) {
 		result = SCAN_PMD_NULL;
 		goto out;
 	}
 
-	__collapse_huge_page_swapin(mm, vma, address, pmd);
+	/*
+	 * __collapse_huge_page_swapin always returns with mmap_sem locked.
+	 * If it fails, release mmap_sem and jump directly out.
+	 * Continuing to collapse causes inconsistency.
+	 */
+	if (!__collapse_huge_page_swapin(mm, vma, address, pmd)) {
+		up_read(&mm->mmap_sem);
+		goto out;
+	}
+
+	up_read(&mm->mmap_sem);
+	/*
+	 * Prevent all access to pagetables with the exception of
+	 * gup_fast later handled by the ptep_clear_flush and the VM
+	 * handled by the anon_vma lock + PG_lock.
+	 */
+	down_write(&mm->mmap_sem);
+	result = hugepage_vma_revalidate(mm, address);
+	if (result)
+		goto out;
 
 	anon_vma_lock_write(vma->anon_vma);