Re: [PATCH mm v4 35/39] kasan: add kasan.vmalloc command line flag

[Andrey Konovalov]

On Tue, Dec 21, 2021 at 3:43 PM Alexander Potapenko <glider@xxxxxxxxxx> wrote:
>
> >
> > +       switch (kasan_arg_vmalloc) {
> > +       case KASAN_ARG_VMALLOC_DEFAULT:
> > +               /* Default to enabling vmalloc tagging. */
> > +               fallthrough;
> > +       case KASAN_ARG_VMALLOC_ON:
> > +               static_branch_enable(&kasan_flag_vmalloc);
> > +               break;
> > +       case KASAN_ARG_VMALLOC_OFF:
> > +               /* Do nothing, kasan_flag_vmalloc keeps its default value. */
> > +               break;
> > +       }
>
> I think we should be setting the default when defining the static key
> (e.g. in this case it should be DEFINE_STATIC_KEY_TRUE), so that:
>  - the _DEFAULT case is always empty;
>  - the _ON case explicitly enables the static branch
>  - the _OFF case explicitly disables the branch
> This way we'll only need to change DEFINE_STATIC_KEY_TRUE to
> DEFINE_STATIC_KEY_FALSE if we want to change the default, but we don't
> have to mess up with the rest of the code.
> Right now the switch statement is confusing, because the _OFF case
> refers to some "default" value, whereas the _DEFAULT one actively
> changes the state.
>
> I see that this code is copied from kasan_flag_stacktrace
> implementation, and my comment also applies there (but I don't insist
> on fixing that one right now).

Will do in v5. Thanks!