Received-SPF: pass (google.com: domain of linux-kernel+bounces-69579-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Precedence: bulk
MIME-Version: 1.0
References: <20240202234057.2085863-1-irogers@google.com> <20240202234057.2085863-3-irogers@google.com>
In-Reply-To: <20240202234057.2085863-3-irogers@google.com>
From: Namhyung Kim <namhyung@kernel.org>
Date: Fri, 16 Feb 2024 16:25:09 -0800
Message-ID: <CAM9d7ci3VO7reyxPc8WOczdoyYYCUshxCJDMZ7wPpHknCubNXQ@mail.gmail.com>
Subject: Re: [PATCH v3 2/8] libperf cpumap: Ensure empty cpumap is NULL from alloc
To: Ian Rogers <irogers@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, 
	Arnaldo Carvalho de Melo <acme@kernel.org>, Mark Rutland <mark.rutland@arm.com>, 
	Alexander Shishkin <alexander.shishkin@linux.intel.com>, Jiri Olsa <jolsa@kernel.org>, 
	Adrian Hunter <adrian.hunter@intel.com>, Suzuki K Poulose <suzuki.poulose@arm.com>, 
	Mike Leach <mike.leach@linaro.org>, James Clark <james.clark@arm.com>, 
	Leo Yan <leo.yan@linaro.org>, John Garry <john.g.garry@oracle.com>, 
	Will Deacon <will@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Darren Hart <dvhart@infradead.org>, 
	Davidlohr Bueso <dave@stgolabs.net>, =?UTF-8?Q?Andr=C3=A9_Almeida?= <andrealmeid@igalia.com>, 
	Kan Liang <kan.liang@linux.intel.com>, K Prateek Nayak <kprateek.nayak@amd.com>, 
	Sean Christopherson <seanjc@google.com>, Paolo Bonzini <pbonzini@redhat.com>, 
	Kajol Jain <kjain@linux.ibm.com>, Athira Rajeev <atrajeev@linux.vnet.ibm.com>, 
	Andrew Jones <ajones@ventanamicro.com>, Alexandre Ghiti <alexghiti@rivosinc.com>, 
	Atish Patra <atishp@rivosinc.com>, "Steinar H. Gunderson" <sesse@google.com>, 
	Yang Jihong <yangjihong1@huawei.com>, Yang Li <yang.lee@linux.alibaba.com>, 
	Changbin Du <changbin.du@huawei.com>, Sandipan Das <sandipan.das@amd.com>, 
	Ravi Bangoria <ravi.bangoria@amd.com>, Paran Lee <p4ranlee@gmail.com>, 
	Nick Desaulniers <ndesaulniers@google.com>, Huacai Chen <chenhuacai@kernel.org>, 
	Yanteng Si <siyanteng@loongson.cn>, linux-perf-users@vger.kernel.org, 
	linux-kernel@vger.kernel.org, coresight@lists.linaro.org, 
	linux-arm-kernel@lists.infradead.org, bpf@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Fri, Feb 2, 2024 at 3:41=E2=80=AFPM Ian Rogers <irogers@google.com> wrot=
e:
>
> Potential corner cases could cause a cpumap to be allocated with size
> 0, but an empty cpumap should be represented as NULL. Add a path in
> perf_cpu_map__alloc to ensure this.
>
> Suggested-by: James Clark <james.clark@arm.com>
> Closes: https://lore.kernel.org/lkml/2cd09e7c-eb88-6726-6169-647dcd0a8101=
@arm.com/
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/lib/perf/cpumap.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/perf/cpumap.c b/tools/lib/perf/cpumap.c
> index ba49552952c5..cae799ad44e1 100644
> --- a/tools/lib/perf/cpumap.c
> +++ b/tools/lib/perf/cpumap.c
> @@ -18,9 +18,13 @@ void perf_cpu_map__set_nr(struct perf_cpu_map *map, in=
t nr_cpus)
>
>  struct perf_cpu_map *perf_cpu_map__alloc(int nr_cpus)
>  {
> -       RC_STRUCT(perf_cpu_map) *cpus =3D malloc(sizeof(*cpus) + sizeof(s=
truct perf_cpu) * nr_cpus);
> +       RC_STRUCT(perf_cpu_map) *cpus;
>         struct perf_cpu_map *result;
>
> +       if (nr_cpus =3D=3D 0)
> +               return NULL;

But allocation failure also returns NULL.  Then callers should check
what's the expected result.

Thanks,
Namhyung

> +
> +       cpus =3D malloc(sizeof(*cpus) + sizeof(struct perf_cpu) * nr_cpus=
);
>         if (ADD_RC_CHK(result, cpus)) {
>                 cpus->nr =3D nr_cpus;
>                 refcount_set(&cpus->refcnt, 1);
> --
> 2.43.0.594.gd9cf4e227d-goog
>