[PATCH 04/10] perf ftrace: Fix failure to set cpumask when only one cpu is present

[Arnaldo Carvalho de Melo]

From: He Zhe <zhe.he@xxxxxxxxxxxxx>

The buffer containing the string used to set cpumask is overwritten at
the end of the 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 the cpumask string size.

Signed-off-by: He Zhe <zhe.he@xxxxxxxxxxxxx>
Tested-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Fixes: dc23103278c5 ("perf ftrace: Add support for -a and -C option")
Link: http://lkml.kernel.org/r/1564734592-15624-1-git-send-email-zhe.he@xxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 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 66d5a6658daf..019312810405 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);
-- 
2.21.0