linux-kernel - Re: [RFC v3 3/7] mm: Use seprintf() instead of less ergonomic APIs

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Message-ID: <CANpmjNNXyyfmYFPYm2LCF_+vdPtWED3xj5gOJPQazpGhBizk5w@mail.gmail.com>
Date: Mon, 7 Jul 2025 16:58:53 +0200
From: Marco Elver <elver@...gle.com>
To: Alejandro Colomar <alx@...nel.org>
Cc: linux-mm@...ck.org, linux-hardening@...r.kernel.org, 
	Kees Cook <kees@...nel.org>, Christopher Bazley <chris.bazley.wg14@...il.com>, 
	shadow <~hallyn/shadow@...ts.sr.ht>, linux-kernel@...r.kernel.org, 
	Andrew Morton <akpm@...ux-foundation.org>, kasan-dev@...glegroups.com, 
	Dmitry Vyukov <dvyukov@...gle.com>, Alexander Potapenko <glider@...gle.com>, Christoph Lameter <cl@...ux.com>, 
	David Rientjes <rientjes@...gle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Harry Yoo <harry.yoo@...cle.com>, 
	Andrew Clayton <andrew@...ital-domain.net>, Sven Schnelle <svens@...ux.ibm.com>, 
	Heiko Carstens <hca@...ux.ibm.com>, Tvrtko Ursulin <tvrtko.ursulin@...lia.com>, 
	"Huang, Ying" <ying.huang@...el.com>, Lee Schermerhorn <lee.schermerhorn@...com>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, 
	Christophe JAILLET <christophe.jaillet@...adoo.fr>, Hyeonggon Yoo <42.hyeyoo@...il.com>, 
	Chao Yu <chao.yu@...o.com>
Subject: Re: [RFC v3 3/7] mm: Use seprintf() instead of less ergonomic APIs

On Mon, 7 Jul 2025 at 16:39, Alejandro Colomar <alx@...nel.org> wrote:
>
> Hi Marco,
>
> On Mon, Jul 07, 2025 at 09:44:09AM +0200, Marco Elver wrote:
> > On Mon, 7 Jul 2025 at 07:06, Alejandro Colomar <alx@...nel.org> wrote:
> > >
> > > While doing this, I detected some anomalies in the existing code:
> > >
> > > mm/kfence/kfence_test.c:
> > >
> > >         -  The last call to scnprintf() did increment 'cur', but it's
> > >            unused after that, so it was dead code.  I've removed the dead
> > >            code in this patch.
> >
> > That was done to be consistent with the other code for readability,
> > and to be clear where the next bytes should be appended (if someone
> > decides to append more). There is no runtime dead code, the compiler
> > optimizes away the assignment. But I'm indifferent, so removing the
> > assignment is fine if you prefer that.
>
> Yeah, I guessed that might be the reason.  I'm fine restoring it if you
> prefer it.  I tend to use -Wunused-but-set-variable, but if it is not
> used here and doesn't trigger, I guess it's fine to keep it.

Feel free to make it warning-free, I guess that's useful.

> > Did you run the tests? Do they pass?
>
> I don't know how to run them.  I've only built the kernel.  If you point
> me to instructions on how to run them, I'll do so.  Thanks!

Should just be CONFIG_KFENCE_KUNIT_TEST=y -- then boot kernel and
check that the test reports "ok".

Thanks,
-- marco