On Mon, May 17, 2021 at 06:17:47AM -0700, Tom Rix wrote:
>
> 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.
>
I think I prefer setting it to 0 because it forces the loop to have
succeeded vs being able to bypass it if the for loop logic was changed.
> > for (...) { }
> > BUG_ON(!best_upa);
> WARN_ON instead?
This is initialization code. So if upa == 0, it really is a problem.
Having 0 units per allocation is bogus.
> > 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
