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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id r14sm14040245qke.47.2019.07.18.13.44.43 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 18 Jul 2019 13:44:43 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 12.4 \(3445.104.11\)) Subject: Re: [PATCH v2] sched/core: silence a warning in sched_init() From: Qian Cai In-Reply-To: <20190625155745.GF3419@hirez.programming.kicks-ass.net> Date: Thu, 18 Jul 2019 16:44:42 -0400 Cc: mingo@redhat.com, Valentin Schneider , LKML Content-Transfer-Encoding: quoted-printable Message-Id: <045C79AE-8A15-4287-8788-BF84AC6BA382@lca.pw> References: <1561466662-22314-1-git-send-email-cai@lca.pw> <20190625135238.GA3419@hirez.programming.kicks-ass.net> <1561471459.5154.70.camel@lca.pw> <20190625142508.GE3419@hirez.programming.kicks-ass.net> <1561475229.5154.74.camel@lca.pw> <20190625155745.GF3419@hirez.programming.kicks-ass.net> To: Peter Zijlstra X-Mailer: Apple Mail (2.3445.104.11) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Jun 25, 2019, at 11:57 AM, Peter Zijlstra = wrote: >=20 > On Tue, Jun 25, 2019 at 11:07:09AM -0400, Qian Cai wrote: >> On Tue, 2019-06-25 at 16:25 +0200, Peter Zijlstra wrote: >>> On Tue, Jun 25, 2019 at 10:04:19AM -0400, Qian Cai wrote: >>>> On Tue, 2019-06-25 at 15:52 +0200, Peter Zijlstra wrote: >>>> Yes, -Wmissing-prototype makes no sense, but = "-Wunused-but-set-variable" is >>>> pretty valid to catch certain developer errors. For example, >>>>=20 >>>> = https://lists.linuxfoundation.org/pipermail/iommu/2019-May/035680.html >>>>=20 >>>>>=20 >>>>> As to this one, ideally the compiler would not be stupid, and = understand >>>>> the below, but alas. >>>>=20 >>>> Pretty sure that won't work, as the compiler will complain = something like, >>>>=20 >>>> ISO C90 forbids mixed declarations and code >>>=20 >>> No, it builds just fine, it's a new block and C allows new variables = at >>> every block start -- with the scope of that block. >>=20 >> I remember I tried that before but recalled the error code wrong. = Here it is, >>=20 >> kernel/sched/core.c:5940:17: warning: unused variable 'ptr' = [-Wunused-variable] >> unsigned long ptr =3D (unsigned = long)kzalloc(alloc_size, >> GFP_NOWAIT); >=20 > Yes, I know, I tried. And GCC is a moron because of it. Actually, not only GCC but clang also don=E2=80=99t understand your = patch. # make CC=3Dclang W=3D1 kernel/sched/core.o kernel/sched/core.c:6384:17: warning: unused variable 'ptr' = [-Wunused-variable] unsigned long ptr =3D (unsigned long)kzalloc(alloc_size, = GFP_NOWAIT); Maybe adding a =E2=80=9C__maybe_unused=E2=80=9D until the day that = compilers are getting smarter.=20=