[PATCH v3 2/2] selftests: sched: skip cs_prctl_test for systems with core scheduling disabled

[Sinadin Shan <sinadin.shan@oracle.com>]

For kernels with CONFIG_SCHED_CORE=n, the sched selftest cs_prctl_test
fails with "Not a core sched system" error. Change this to gracefully
skip the test for systems with core scheduling disabled. Exiting early
would also ensure failures reported in obtaining cookie are valid
failures and not because core scheduling isn't supported.

Skip cs_prctl_test for systems with CONFIG_SCHED_CORE=n

Signed-off-by: Sinadin Shan <sinadin.shan@oracle.com>
---
 tools/testing/selftests/sched/cs_prctl_test.c | 34 ++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/sched/cs_prctl_test.c b/tools/testing/selftests/sched/cs_prctl_test.c
index 52d97fae4dbd8..5b0047b50e640 100644
--- a/tools/testing/selftests/sched/cs_prctl_test.c
+++ b/tools/testing/selftests/sched/cs_prctl_test.c
@@ -109,6 +109,36 @@ static void handle_usage(int rc, char *msg)
 	exit(rc);
 }
 
+static void check_core_sched(void)
+{
+	unsigned long long cookie;
+	int ret, num_max_process;
+	char buffer[32];
+
+	FILE *fp = fopen("/proc/sys/kernel/pid_max", "r");
+
+	if (fp == NULL) {
+		perror("Failed to obtain max process number");
+		exit(EXIT_FAILURE);
+	}
+
+	if (fgets(buffer, sizeof(buffer), fp) == NULL) {
+		fclose(fp);
+		exit(EXIT_FAILURE);
+	}
+
+	num_max_process = atoi(buffer);
+	fclose(fp);
+
+	ret = prctl(PR_SCHED_CORE, PR_SCHED_CORE_GET, num_max_process+1, PIDTYPE_PID,
+			(unsigned long)&cookie);
+	if (ret == -1 && errno != ESRCH) {
+		perror("prctl failed");
+		printf("Core sched not supported, hence skipping tests\n");
+		exit(4);
+	}
+}
+
 static unsigned long get_cs_cookie(int pid)
 {
 	unsigned long long cookie;
@@ -117,7 +147,7 @@ static unsigned long get_cs_cookie(int pid)
 	ret = prctl(PR_SCHED_CORE, PR_SCHED_CORE_GET, pid, PIDTYPE_PID,
 		    (unsigned long)&cookie);
 	if (ret) {
-		printf("Not a core sched system\n");
+		printf("Failed to get cookie\n");
 		return -1UL;
 	}
 
@@ -270,6 +300,8 @@ int main(int argc, char *argv[])
 	if (keypress)
 		delay = -1;
 
+	check_core_sched();
+
 	srand(time(NULL));
 
 	/* put into separate process group */
-- 
2.43.5