Re: [PATCH linux-next] mm/hugetlb: fix warning in alloc_huge_page/dequeue_huge_page_vma

[Konstantin Khlebnikov]

Andrew Morton wrote:
> On Tue, 17 Apr 2012 16:28:19 +0400
> Konstantin Khlebnikov<khlebnikov@xxxxxxxxxx>  wrote:
>
> > This patch fixes gcc warning (and bug?) introduced in linux-next commit cc9a6c877
> > ("cpuset: mm: reduce large amounts of memory barrier related damage v3")
> >
> > Local variable "page" can be uninitialized if nodemask from vma policy does not
> > intersects with nodemask from cpuset. Even if it wouldn't happens it's better to
> > initialize this variable explicitly than to introduce kernel oops on weird corner case.
> >
> > mm/hugetlb.c: In function ___alloc_huge_page___:
> > mm/hugetlb.c:1135:5: warning: ___page___ may be used uninitialized in this function
> >
> > ...
> >
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -532,7 +532,7 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
> >   				struct vm_area_struct *vma,
> >   				unsigned long address, int avoid_reserve)
> >   {
> > -	struct page *page;
> > +	struct page *page = NULL;
> >   	struct mempolicy *mpol;
> >   	nodemask_t *nodemask;
> >   	struct zonelist *zonelist;
>
> hm, that's a pretty blatant use-uninitialised bug.  I wonder why so few
> gcc versions report it.  Mine doesn't.

I'm using latest gcc-4.7

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