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From:   Andrey Konovalov <andreyknvl@gmail.com>
Date:   Thu, 30 Dec 2021 20:11:40 +0100
Message-ID: <CA+fCnZd-Z6ySi0dqkZjgEfD2sRDvDiHc5bgxDF=x_yB1+kOLJw@mail.gmail.com>
Subject: Re: [PATCH mm v4 35/39] kasan: add kasan.vmalloc command line flag
To:     Alexander Potapenko <glider@google.com>
Cc:     andrey.konovalov@linux.dev, Marco Elver <elver@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux Memory Management List <linux-mm@kvack.org>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Peter Collingbourne <pcc@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Andrey Konovalov <andreyknvl@google.com>
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On Tue, Dec 21, 2021 at 3:43 PM Alexander Potapenko <glider@google.com> 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!