linux-kernel - Re: [PATCH v3 2/8] libperf cpumap: Ensure empty cpumap is NULL from alloc

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Message-ID: <CAM9d7ci3VO7reyxPc8WOczdoyYYCUshxCJDMZ7wPpHknCubNXQ@mail.gmail.com>
Date: Fri, 16 Feb 2024 16:25:09 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, Suzuki K Poulose <suzuki.poulose@....com>, 
	Mike Leach <mike.leach@...aro.org>, James Clark <james.clark@....com>, 
	Leo Yan <leo.yan@...aro.org>, John Garry <john.g.garry@...cle.com>, 
	Will Deacon <will@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Darren Hart <dvhart@...radead.org>, 
	Davidlohr Bueso <dave@...olabs.net>, André Almeida <andrealmeid@...lia.com>, 
	Kan Liang <kan.liang@...ux.intel.com>, K Prateek Nayak <kprateek.nayak@....com>, 
	Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Kajol Jain <kjain@...ux.ibm.com>, Athira Rajeev <atrajeev@...ux.vnet.ibm.com>, 
	Andrew Jones <ajones@...tanamicro.com>, Alexandre Ghiti <alexghiti@...osinc.com>, 
	Atish Patra <atishp@...osinc.com>, "Steinar H. Gunderson" <sesse@...gle.com>, 
	Yang Jihong <yangjihong1@...wei.com>, Yang Li <yang.lee@...ux.alibaba.com>, 
	Changbin Du <changbin.du@...wei.com>, Sandipan Das <sandipan.das@....com>, 
	Ravi Bangoria <ravi.bangoria@....com>, Paran Lee <p4ranlee@...il.com>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Huacai Chen <chenhuacai@...nel.org>, 
	Yanteng Si <siyanteng@...ngson.cn>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org, coresight@...ts.linaro.org, 
	linux-arm-kernel@...ts.infradead.org, bpf@...r.kernel.org
Subject: Re: [PATCH v3 2/8] libperf cpumap: Ensure empty cpumap is NULL from alloc

On Fri, Feb 2, 2024 at 3:41 PM Ian Rogers <irogers@...gle.com> wrote:
>
> 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@....com>
> Closes: https://lore.kernel.org/lkml/2cd09e7c-eb88-6726-6169-647dcd0a8101@arm.com/
> Signed-off-by: Ian Rogers <irogers@...gle.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, int nr_cpus)
>
>  struct perf_cpu_map *perf_cpu_map__alloc(int nr_cpus)
>  {
> -       RC_STRUCT(perf_cpu_map) *cpus = malloc(sizeof(*cpus) + sizeof(struct perf_cpu) * nr_cpus);
> +       RC_STRUCT(perf_cpu_map) *cpus;
>         struct perf_cpu_map *result;
>
> +       if (nr_cpus == 0)
> +               return NULL;

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

Thanks,
Namhyung

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