linux-kernel - Re: [PATCH v2 1/6] lib/stackdepot: allow requesting early initialization dynamically

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Date:   Wed, 2 Mar 2022 19:15:32 +0100
From:   Marco Elver <elver@...gle.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     David Rientjes <rientjes@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Pekka Enberg <penberg@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        patches@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Oliver Glitta <glittao@...il.com>,
        Faiyaz Mohammed <faiyazm@...eaurora.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Imran Khan <imran.f.khan@...cle.com>
Subject: Re: [PATCH v2 1/6] lib/stackdepot: allow requesting early
 initialization dynamically

On Wed, 2 Mar 2022 at 19:02, Vlastimil Babka <vbabka@...e.cz> wrote:
[...]
> > Similarly, for stack_depot_want_early_init, where instead you could
> > simply provide stack_depot_want_early_init() as a function, which simply
> > sets a boolean __stack_depot_want_early_init. If !STACKDEPOT, it'll also
> > just be a no-op function.
>
> Yeah, makes sense. I guess I have patch 3/6 wrong now anyway as with
> !STACKDEPOT it should fail linking due to missing stack_depot_want_early_init...

Right. It probably still worked because the compiler likely optimizes
out the dead call, but you never know...

> >> +bool stack_depot_want_early_init = false;
> >> +
> >
> > This can be __initdata, right?
>
> I initially thought so too, but in include/linux/init.h found
>  * Don't forget to initialize data not at file scope, i.e. within a function,
>  * as gcc otherwise puts the data into the bss section and not into the init
>  * section.
> But maybe that's just outdated as everyone seems to init them at file scope.

I think that comment is just about static variables inside functions?
Here it's at file scope, so that caveat shouldn't apply. As an aside,
you could omit '= false' because it'd zero-init by default.

Thanks,
-- Marco