Re: [PATCH] percpu: initialize best_upa variable

[Tom Rix]

On 5/16/21 7:05 PM, Dennis Zhou wrote:
> Hello,
>
> On Sat, May 15, 2021 at 11:08:17AM -0700, trix@xxxxxxxxxx wrote:
> > From: Tom Rix <trix@xxxxxxxxxx>
> >
> > Static analysis reports this problem
> > percpu.c:2945:6: warning: Assigned value is garbage or undefined
> >          upa = best_upa;
> >              ^ ~~~~~~~~
> > best_upa may not be set, so initialize it.
> >
> > Signed-off-by: Tom Rix <trix@xxxxxxxxxx>
> > ---
> >   mm/percpu.c | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/mm/percpu.c b/mm/percpu.c
> > index a257c3efdf18b..6578b706fae81 100644
> > --- a/mm/percpu.c
> > +++ b/mm/percpu.c
> > @@ -2916,6 +2916,7 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
> >   	 * Related to atom_size, which could be much larger than the unit_size.
> >   	 */
> >   	last_allocs = INT_MAX;
> > +	best_upa = max_upa;
> >   	for (upa = max_upa; upa; upa--) {
> >   		int allocs = 0, wasted = 0;
> >   
> > --
> > 2.26.3
> I think the proper fix would be:
>
> best_upa = 0;

I was looking for initializing with something that would work.

> for (...) { }
> BUG_ON(!best_upa);
WARN_ON instead?
> upa = best_upa;
>
> If you're fine with this I'll make the changes and apply it to
> for-5.13-fixes.
>
> Can you also tell me what static analysis tool produced this? I'm just a
> little curious because this code hasn't changed in several years so I'd
> have expected some static analyzer to have caught this by now.

Clang 10

Tom

> Thanks,
> Dennis