linux-kernel - Re: [PATCH 1/2] perf: Fix failure to set cpumask when only one cpu

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Message-ID: <20190802130607.GA27223@krava>
Date:   Fri, 2 Aug 2019 15:06:07 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     zhe.he@...driver.com
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, namhyung@...nel.org,
        kan.liang@...ux.intel.com, eranian@...gle.com,
        alexey.budankov@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] perf: Fix failure to set cpumask when only one cpu

On Fri, Aug 02, 2019 at 04:29:51PM +0800, zhe.he@...driver.com wrote:
> From: He Zhe <zhe.he@...driver.com>
> 
> The buffer containing string used to set cpumask is overwritten by end of
> string later in cpu_map__snprint_mask due to not enough memory space, when
> there is only one cpu. And thus causes the following failure.
> 
> $ perf ftrace ls
> failed to reset ftrace
> 
> This patch fixes the calculation of cpumask string size.
> 
> Signed-off-by: He Zhe <zhe.he@...driver.com>
> ---
>  tools/perf/builtin-ftrace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> index 66d5a66..0193128 100644
> --- a/tools/perf/builtin-ftrace.c
> +++ b/tools/perf/builtin-ftrace.c
> @@ -173,7 +173,7 @@ static int set_tracing_cpumask(struct cpu_map *cpumap)
>  	int last_cpu;
>  
>  	last_cpu = cpu_map__cpu(cpumap, cpumap->nr - 1);
> -	mask_size = (last_cpu + 3) / 4 + 1;
> +	mask_size = last_cpu / 4 + 2; /* one more byte for EOS */
>  	mask_size += last_cpu / 32; /* ',' is needed for every 32th cpus */

ugh..  why do we care about last_cpu value in here at all?

feels like using static buffer would be more reasonable

jirka

>  
>  	cpumask = malloc(mask_size);
> -- 
> 2.7.4
>