M_MERGE_ANY, mm);
 		mmap_read_unlock(mm);
 		mmdrop(mm);
 	} else {
@@ -2736,12 +2742,20 @@ static int __ksm_del_vma(struct vm_area_struct *vma)
  *
  * Returns: @vm_flags possibly updated to mark mergeable.
  */
-vm_flags_t ksm_vma_flags(const struct mm_struct *mm, const struct file *file,
+vm_flags_t ksm_vma_flags(struct mm_struct *mm, const struct file *file,
 			 vm_flags_t vm_flags)
 {
 	if (mm_flags_test(MMF_VM_MERGE_ANY, mm) &&
-	    __ksm_should_add_vma(file, vm_flags))
+	    __ksm_should_add_vma(file, vm_flags)) {
 		vm_flags |= VM_MERGEABLE;
+		/*
+		 * Generally, the flags here always include MMF_VM_MERGEABLE.
+		 * However, in rare cases, this flag may be cleared by ksmd who
+		 * scans a cycle without finding any mergeable vma.
+		 */
+		if (unlikely(!mm_flags_test(MMF_VM_MERGEABLE, mm)))
+			__ksm_enter(mm);
+	}

 	return vm_flags;
 }
-- 
2.25.1[PATCH linux-next v2 1/2] mm/ksm: fix exec/fork inheritance support for prctl<xu.xin16@zte.com.cn> undefined<xu.xin16@zte.com.cn>, <akpm@linux-foundation.org>, <david@redhat.com>, <shr@devkernel.io> undefined undefined undefined undefined undefined undefined undefined undefined undefined