perf tools: No need to unconditionally read the max_stack sysctls

Let tools that need to have those variables with the sysctl current
values use a function that will read them.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-1ljj3oeo5kpt2n1icfd9vowe@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evsel.c

@@ -2862,7 +2862,7 @@ int perf_evsel__open_strerror(struct perf_evsel *evsel, struct target *target,
 			return scnprintf(msg, size,
 					 "Not enough memory to setup event with callchain.\n"
 					 "Hint: Try tweaking /proc/sys/kernel/perf_event_max_stack\n"
-					 "Hint: Current value: %d", sysctl_perf_event_max_stack);
+					 "Hint: Current value: %d", sysctl__max_stack());
 		break;
 	case ENODEV:
 		if (target->cpu_list)

tools/perf/util/util.c

@@ -62,6 +62,19 @@ int cacheline_size(void)
 int sysctl_perf_event_max_stack = PERF_MAX_STACK_DEPTH;
 int sysctl_perf_event_max_contexts_per_stack = PERF_MAX_CONTEXTS_PER_STACK;
 
+int sysctl__max_stack(void)
+{
+	int value;
+
+	if (sysctl__read_int("kernel/perf_event_max_stack", &value) == 0)
+		sysctl_perf_event_max_stack = value;
+
+	if (sysctl__read_int("kernel/perf_event_max_contexts_per_stack", &value) == 0)
+		sysctl_perf_event_max_contexts_per_stack = value;
+
+	return sysctl_perf_event_max_stack;
+}
+
 bool test_attr__enabled;
 
 bool perf_host  = true;

tools/perf/util/util.h

@@ -45,6 +45,8 @@ int hex2u64(const char *ptr, u64 *val);
 extern unsigned int page_size;
 int __pure cacheline_size(void);
 
+int sysctl__max_stack(void);
+
 int fetch_kernel_version(unsigned int *puint,
 			 char *str, size_t str_sz);
 #define KVER_VERSION(x)		(((x) >> 16) & 0xff)