linux-kernel - Re: [PATCH v2 4/8] selftests/mm: Add -Wunused family of flags

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Message-ID: <57c816d6-a9ba-47c9-8f40-3978580b7f67@arm.com>
Date: Mon, 18 Aug 2025 10:16:35 +0200
From: Kevin Brodsky <kevin.brodsky@....com>
To: Muhammad Usama Anjum <usama.anjum@...labora.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...hat.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Jason Gunthorpe <jgg@...pe.ca>, John Hubbard <jhubbard@...dia.com>,
 Peter Xu <peterx@...hat.com>, Leon Romanovsky <leon@...nel.org>,
 Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
 Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
 Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
 <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Alexandre Ghiti <alex@...ti.fr>, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-riscv@...ts.infradead.org, Shuah Khan <shuah@...nel.org>
Cc: kernel@...labora.com
Subject: Re: [PATCH v2 4/8] selftests/mm: Add -Wunused family of flags

On 31/07/2025 18:01, Muhammad Usama Anjum wrote:
> [...]
>
> diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
> index 23d4bf6215465..d75f1effcb791 100644
> --- a/tools/testing/selftests/mm/Makefile
> +++ b/tools/testing/selftests/mm/Makefile
> @@ -20,7 +20,6 @@ endif
>  # thus tricking Make (and you!) into believing that All Is Well, in subsequent
>  # make invocations:
>  .DELETE_ON_ERROR:
> -
>  # Avoid accidental wrong builds, due to built-in rules working just a little
>  # bit too well--but not quite as well as required for our situation here.
>  #
> @@ -35,6 +34,7 @@ MAKEFLAGS += --no-builtin-rules
>  
>  CFLAGS = -Wall -O2 -I $(top_srcdir) $(EXTRA_CFLAGS) $(KHDR_INCLUDES) $(TOOLS_INCLUDES)
>  CFLAGS += -Wunreachable-code
> +CFLAGS += -Wunused  -Wunused-parameter -Wunused-function -Wunused-label -Wunused-variable -Wunused-value

-Wall implies all of these except -Wunused-parameter (at least according
to gcc(1)).

As to -Wunused-parameter I am frankly not convinced it's worth the
hassle. We're getting 90 lines changed in patch 6-8 just to mark
parameters as unused, in other words noise to keep the compiler happy.
It is not enabled by default in the kernel proper precisely because it
is so noisy when callbacks are involved.

Patch 5 is clearly an improvement, but I'd rather take it without
actually enabling -Wunused-parameter. The rest of this patch isn't that
useful either IMHO.

- Kevin