Re: [BUG]: mm/vmalloc: uninitialized variable access in pcpu_get_vm_areas

[Roman Penyaev]

On 2019-06-17 16:44, Arnd Bergmann wrote:
> On Mon, Jun 17, 2019 at 4:12 PM Uladzislau Rezki <urezki@xxxxxxxxx> 
> wrote:
> > On Mon, Jun 17, 2019 at 02:14:11PM +0200, Arnd Bergmann wrote:
> > > gcc points out some obviously broken code in linux-next
> > >
> > > mm/vmalloc.c: In function 'pcpu_get_vm_areas':
> > > mm/vmalloc.c:991:4: error: 'lva' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> > >     insert_vmap_area_augment(lva, &va->rb_node,
> > >     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >      &free_vmap_area_root, &free_vmap_area_list);
> > >      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > mm/vmalloc.c:916:20: note: 'lva' was declared here
> > >   struct vmap_area *lva;
> > >                     ^~~
> > >
> > > Remove the obviously broken code. This is almost certainly
> > > not the correct solution, but it's what I have applied locally
> > > to get a clean build again.
> > >
> > > Please fix this properly.
> > >
>
> > >
> > Please do not apply this. It will just break everything.
>
> As I wrote in my description, this was purely meant as a bug
> report, not a patch to be applied.

That's a perfect way to attract attention! :)

> > As Roman pointed we can just set lva = NULL; in the beginning to make 
> > GCC happy.
> > For some reason GCC decides that it can be used uninitialized, but 
> > that
> > is not true.
>
> I got confused by the similarly named FL_FIT_TYPE/NE_FIT_TYPE

Names are indeed very confusing, that is true.  Very easy to mix up 
things.

--
Roman