samples/bpf: Check the result of system()

[ Upstream commit 492b7e894587c151be681f86d4d1d086375f7b45 ]

To avoid the below build warning message,
use new generate_load() checking the return value.

  ignoring return value of ‘system’, declared with attribute warn_unused_result

And it also refactors the duplicate code of both
test_perf_event_all_cpu() and test_perf_event_task()

Cc: Teng Qin <qinteng@fb.com>
Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

samples/bpf/trace_event_user.c

@@ -121,6 +121,16 @@ static void print_stacks(void)
 	}
 }
 
+static inline int generate_load(void)
+{
+	if (system("dd if=/dev/zero of=/dev/null count=5000k status=none") < 0) {
+		printf("failed to generate some load with dd: %s\n", strerror(errno));
+		return -1;
+	}
+
+	return 0;
+}
+
 static void test_perf_event_all_cpu(struct perf_event_attr *attr)
 {
 	int nr_cpus = sysconf(_SC_NPROCESSORS_CONF);
@@ -138,7 +148,11 @@ static void test_perf_event_all_cpu(struct perf_event_attr *attr)
 		assert(ioctl(pmu_fd[i], PERF_EVENT_IOC_SET_BPF, prog_fd[0]) == 0);
 		assert(ioctl(pmu_fd[i], PERF_EVENT_IOC_ENABLE) == 0);
 	}
-	system("dd if=/dev/zero of=/dev/null count=5000k status=none");
+
+	if (generate_load() < 0) {
+		error = 1;
+		goto all_cpu_err;
+	}
 	print_stacks();
 all_cpu_err:
 	for (i--; i >= 0; i--) {
@@ -152,7 +166,7 @@ all_cpu_err:
 
 static void test_perf_event_task(struct perf_event_attr *attr)
 {
-	int pmu_fd;
+	int pmu_fd, error = 0;
 
 	/* open task bound event */
 	pmu_fd = sys_perf_event_open(attr, 0, -1, -1, 0);
@@ -162,10 +176,17 @@ static void test_perf_event_task(struct perf_event_attr *attr)
 	}
 	assert(ioctl(pmu_fd, PERF_EVENT_IOC_SET_BPF, prog_fd[0]) == 0);
 	assert(ioctl(pmu_fd, PERF_EVENT_IOC_ENABLE) == 0);
-	system("dd if=/dev/zero of=/dev/null count=5000k status=none");
+
+	if (generate_load() < 0) {
+		error = 1;
+		goto err;
+	}
 	print_stacks();
+err:
 	ioctl(pmu_fd, PERF_EVENT_IOC_DISABLE);
 	close(pmu_fd);
+	if (error)
+		int_exit(0);
 }
 
 static void test_bpf_perf_event(void)