mm: zero out the vma in vma_init()

Rather than in vm_area_alloc().  To ensure that the various oddball
stack-based vmas are in a good state.  Some of the callers were zeroing
them out, others were not.

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/fork.c

@@ -310,8 +310,9 @@ static struct kmem_cache *mm_cachep;
 
 struct vm_area_struct *vm_area_alloc(struct mm_struct *mm)
 {
-	struct vm_area_struct *vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
+	struct vm_area_struct *vma;
 
+	vma = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
 	if (vma)
 		vma_init(vma, mm);
 	return vma;