mm: make vm_area_dup() actually copy the old vma data

.. and re-initialize th eanon_vma_chain head.

This removes some boiler-plate from the users, and also makes it clear
why it didn't need use the 'zalloc()' version.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/fork.c

@@ -315,7 +315,13 @@ struct vm_area_struct *vm_area_alloc(void)
 
 struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
 {
-	return kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
+	struct vm_area_struct *new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
+
+	if (new) {
+		*new = *orig;
+		INIT_LIST_HEAD(&new->anon_vma_chain);
+	}
+	return new;
 }
 
 void vm_area_free(struct vm_area_struct *vma)
@@ -473,8 +479,6 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
 		tmp = vm_area_dup(mpnt);
 		if (!tmp)
 			goto fail_nomem;
-		*tmp = *mpnt;
-		INIT_LIST_HEAD(&tmp->anon_vma_chain);
 		retval = vma_dup_policy(mpnt, tmp);
 		if (retval)
 			goto fail_nomem_policy;

mm/mmap.c

@@ -2624,11 +2624,6 @@ int __split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
 	if (!new)
 		return -ENOMEM;
 
-	/* most fields are the same, copy all, and then fixup */
-	*new = *vma;
-
-	INIT_LIST_HEAD(&new->anon_vma_chain);
-
 	if (new_below)
 		new->vm_end = addr;
 	else {
@@ -3205,13 +3200,11 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 		new_vma = vm_area_dup(vma);
 		if (!new_vma)
 			goto out;
-		*new_vma = *vma;
 		new_vma->vm_start = addr;
 		new_vma->vm_end = addr + len;
 		new_vma->vm_pgoff = pgoff;
 		if (vma_dup_policy(vma, new_vma))
 			goto out_free_vma;
-		INIT_LIST_HEAD(&new_vma->anon_vma_chain);
 		if (anon_vma_clone(new_vma, vma))
 			goto out_free_mempol;
 		if (new_vma->vm_file)

mm/nommu.c

@@ -1476,7 +1476,6 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
 	}
 
 	/* most fields are the same, copy all, and then fixup */
-	*new = *vma;
 	*region = *vma->vm_region;
 	new->vm_region = region;