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

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Date:   Fri, 2 Aug 2019 16:29:51 +0800
From:   <zhe.he@...driver.com>
To:     <peterz@...radead.org>, <mingo@...hat.com>, <acme@...nel.org>,
        <alexander.shishkin@...ux.intel.com>, <jolsa@...hat.com>,
        <namhyung@...nel.org>, <kan.liang@...ux.intel.com>,
        <eranian@...gle.com>, <alexey.budankov@...ux.intel.com>,
        <linux-kernel@...r.kernel.org>, <zhe.he@...driver.com>
Subject: [PATCH 1/2] perf: Fix failure to set cpumask when only one cpu

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 */
 
 	cpumask = malloc(mask_size);
-- 
2.7.4