linux-kernel - Re: [PATCH v2 14/19] lib/stackdepot, kasan: add flags to __stack_depot

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Message-ID: <CA+fCnZdzpHEPnFa1A5TtFu_si3RbQrBEFXHhALEtnVR4nhfzEw@mail.gmail.com>
Date:   Mon, 23 Oct 2023 18:17:12 +0200
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     andrey.konovalov@...ux.dev, Marco Elver <elver@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>, kasan-dev@...glegroups.com,
        Evgenii Stepanov <eugenis@...gle.com>,
        Oscar Salvador <osalvador@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH v2 14/19] lib/stackdepot, kasan: add flags to
 __stack_depot_save and rename

On Mon, Oct 9, 2023 at 12:10 PM Alexander Potapenko <glider@...gle.com> wrote:
>
> On Wed, Sep 13, 2023 at 7:17 PM <andrey.konovalov@...ux.dev> wrote:
> >
> > From: Andrey Konovalov <andreyknvl@...gle.com>
> >
> > Change the bool can_alloc argument of __stack_depot_save to a
> > u32 argument that accepts a set of flags.
> >
> > The following patch will add another flag to stack_depot_save_flags
> > besides the existing STACK_DEPOT_FLAG_CAN_ALLOC.
> >
> > Also rename the function to stack_depot_save_flags, as __stack_depot_save
> > is a cryptic name,
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> Reviewed-by: Alexander Potapenko <glider@...gle.com>
> (assuming you'll address Marco's comment)
>
> ...
>
> >  void kasan_record_aux_stack_noalloc(void *addr)
> >  {
> > -       return __kasan_record_aux_stack(addr, false);
> > +       return __kasan_record_aux_stack(addr, 0);
>
> Maybe make the intent to not allocate more explicit by declaring some
> STACK_DEPOT_FLAG_CAN_NOT_ALLOC = 0?
> (Leaving this up to you)

The next patch adds another flag, so STACK_DEPOT_FLAG_CAN_NOT_ALLOC is
probably not the best name. I could add something like
STACK_DEPOT_FLAG_NONE, but I think this might create an impression
that there's some kind of NONE flag that affects the behavior of
stack_depot_save_flags in a special way.

I think we can just keep the value as 0, as it seems what the kernel
does in similar cases. E.g. for slab_flags_t, the kernel passes 0 to
kmem_cache_create when there are no special flags required.

Thanks!