[PATCH v2 2/2] selftests/sched: Retry PR_SCHED_CORE_GET on EBUSY

[Hui Su <sh_def@163.com>]

During early boot, the pointer hash key may not be initialized when
PR_SCHED_CORE_GET is called. With the preceding kernel fix, GET reports
EBUSY until the pointer hash key becomes available.

Retry the operation for up to one second when it returns EBUSY. Keep the
syscall status separate from the returned cookie and abort the test if
the GET still fails, so an error value cannot be compared as a valid
cookie. Report other errors immediately instead of describing every
failed GET as an unsupported core scheduling system.

cs_prctl_test passes on x86_64 with normal random initialization.

Signed-off-by: Hui Su <sh_def@163.com>
---
v2:
- Return cookie values directly from the fatal error helper to keep the
  selftest comparisons compact.
- Avoid sleeping after the final retry.

 tools/testing/selftests/sched/cs_prctl_test.c | 93 +++++++++++++------
 1 file changed, 63 insertions(+), 30 deletions(-)

diff --git a/tools/testing/selftests/sched/cs_prctl_test.c b/tools/testing/selftests/sched/cs_prctl_test.c
index 52d97fae4dbd..7bd0bc262a6b 100644
--- a/tools/testing/selftests/sched/cs_prctl_test.c
+++ b/tools/testing/selftests/sched/cs_prctl_test.c
@@ -51,6 +51,8 @@ static pid_t gettid(void)
 
 #define MAX_PROCESSES 128
 #define MAX_THREADS   128
+#define CORE_COOKIE_RETRIES	100
+#define CORE_COOKIE_RETRY_US	10000
 
 static const char USAGE[] = "cs_prctl_test [options]\n"
 "    options:\n"
@@ -109,19 +111,43 @@ static void handle_usage(int rc, char *msg)
 	exit(rc);
 }
 
-static unsigned long get_cs_cookie(int pid)
+static int get_cs_cookie(int pid, unsigned long long *cookie)
 {
-	unsigned long long cookie;
-	int ret;
+	int i, ret, err = 0;
 
-	ret = prctl(PR_SCHED_CORE, PR_SCHED_CORE_GET, pid, PIDTYPE_PID,
-		    (unsigned long)&cookie);
-	if (ret) {
-		printf("Not a core sched system\n");
-		return -1UL;
+	for (i = 0; i < CORE_COOKIE_RETRIES; i++) {
+		ret = prctl(PR_SCHED_CORE, PR_SCHED_CORE_GET, pid, PIDTYPE_PID,
+			    (unsigned long)cookie);
+		if (!ret)
+			return 0;
+
+		err = errno;
+		if (err != EBUSY || i == CORE_COOKIE_RETRIES - 1)
+			break;
+
+		usleep(CORE_COOKIE_RETRY_US);
 	}
 
-	return cookie;
+	if (err == EBUSY)
+		printf("Timed out waiting for core sched cookie\n");
+	else
+		printf("Failed to get core sched cookie: %s\n", strerror(err));
+
+	return err;
+}
+
+static unsigned long long get_cs_cookie_or_die(int pid)
+{
+	unsigned long long cookie;
+	int err;
+
+	err = get_cs_cookie(pid, &cookie);
+	if (!err)
+		return cookie;
+
+	errno = err;
+	handle_error("get core sched cookie");
+	__builtin_unreachable();
 }
 
 static int child_func_thread(void __attribute__((unused))*arg)
@@ -202,15 +228,16 @@ void disp_processes(int num_processes, struct child_args proc[])
 {
 	int i, j;
 
-	printf("tid=%d, / tgid=%d / pgid=%d: %lx\n", gettid(), getpid(), getpgid(0),
-	       get_cs_cookie(getpid()));
+	printf("tid=%d, / tgid=%d / pgid=%d: %llx\n", gettid(), getpid(), getpgid(0),
+	       get_cs_cookie_or_die(getpid()));
 
 	for (i = 0; i < num_processes; ++i) {
-		printf("    tid=%d, / tgid=%d / pgid=%d: %lx\n", proc[i].cpid, proc[i].cpid,
-		       getpgid(proc[i].cpid), get_cs_cookie(proc[i].cpid));
+		printf("    tid=%d, / tgid=%d / pgid=%d: %llx\n", proc[i].cpid, proc[i].cpid,
+		       getpgid(proc[i].cpid), get_cs_cookie_or_die(proc[i].cpid));
 		for (j = 0; j < proc[i].num_threads; ++j) {
-			printf("        tid=%d, / tgid=%d / pgid=%d: %lx\n", proc[i].thr_tids[j],
-			       proc[i].cpid, getpgid(0), get_cs_cookie(proc[i].thr_tids[j]));
+			printf("        tid=%d, / tgid=%d / pgid=%d: %llx\n", proc[i].thr_tids[j],
+			       proc[i].cpid, getpgid(0),
+			       get_cs_cookie_or_die(proc[i].thr_tids[j]));
 		}
 	}
 	puts("\n");
@@ -280,30 +307,32 @@ int main(int argc, char *argv[])
 	create_processes(num_processes, num_threads, procs);
 	need_cleanup = 1;
 	disp_processes(num_processes, procs);
-	validate(get_cs_cookie(0) == 0);
+	validate(get_cs_cookie_or_die(0) == 0);
 
 	printf("\n## Set a cookie on entire process group\n");
 	if (_prctl(PR_SCHED_CORE, PR_SCHED_CORE_CREATE, 0, PIDTYPE_PGID, 0) < 0)
 		handle_error("core_sched create failed -- PGID");
 	disp_processes(num_processes, procs);
 
-	validate(get_cs_cookie(0) != 0);
+	validate(get_cs_cookie_or_die(0) != 0);
 
 	/* get a random process pid */
 	pidx = rand() % num_processes;
 	pid = procs[pidx].cpid;
 
-	validate(get_cs_cookie(0) == get_cs_cookie(pid));
-	validate(get_cs_cookie(0) == get_cs_cookie(procs[pidx].thr_tids[0]));
+	validate(get_cs_cookie_or_die(0) == get_cs_cookie_or_die(pid));
+	validate(get_cs_cookie_or_die(0) ==
+		 get_cs_cookie_or_die(procs[pidx].thr_tids[0]));
 
 	printf("\n## Set a new cookie on entire process/TGID [%d]\n", pid);
 	if (_prctl(PR_SCHED_CORE, PR_SCHED_CORE_CREATE, pid, PIDTYPE_TGID, 0) < 0)
 		handle_error("core_sched create failed -- TGID");
 	disp_processes(num_processes, procs);
 
-	validate(get_cs_cookie(0) != get_cs_cookie(pid));
-	validate(get_cs_cookie(pid) != 0);
-	validate(get_cs_cookie(pid) == get_cs_cookie(procs[pidx].thr_tids[0]));
+	validate(get_cs_cookie_or_die(0) != get_cs_cookie_or_die(pid));
+	validate(get_cs_cookie_or_die(pid) != 0);
+	validate(get_cs_cookie_or_die(pid) ==
+		 get_cs_cookie_or_die(procs[pidx].thr_tids[0]));
 
 	printf("\n## Copy the cookie of current/PGID[%d], to pid [%d] as PIDTYPE_PID\n",
 	       getpid(), pid);
@@ -311,9 +340,10 @@ int main(int argc, char *argv[])
 		handle_error("core_sched share to itself failed -- PID");
 	disp_processes(num_processes, procs);
 
-	validate(get_cs_cookie(0) == get_cs_cookie(pid));
-	validate(get_cs_cookie(pid) != 0);
-	validate(get_cs_cookie(pid) != get_cs_cookie(procs[pidx].thr_tids[0]));
+	validate(get_cs_cookie_or_die(0) == get_cs_cookie_or_die(pid));
+	validate(get_cs_cookie_or_die(pid) != 0);
+	validate(get_cs_cookie_or_die(pid) !=
+		 get_cs_cookie_or_die(procs[pidx].thr_tids[0]));
 
 	printf("\n## Copy cookie from a thread [%d] to current/PGID [%d] as PIDTYPE_PID\n",
 	       procs[pidx].thr_tids[0], getpid());
@@ -322,17 +352,20 @@ int main(int argc, char *argv[])
 		handle_error("core_sched share from thread failed -- PID");
 	disp_processes(num_processes, procs);
 
-	validate(get_cs_cookie(0) == get_cs_cookie(procs[pidx].thr_tids[0]));
-	validate(get_cs_cookie(pid) != get_cs_cookie(procs[pidx].thr_tids[0]));
+	validate(get_cs_cookie_or_die(0) ==
+		 get_cs_cookie_or_die(procs[pidx].thr_tids[0]));
+	validate(get_cs_cookie_or_die(pid) !=
+		 get_cs_cookie_or_die(procs[pidx].thr_tids[0]));
 
 	printf("\n## Copy cookie from current [%d] to current as pidtype PGID\n", getpid());
 	if (_prctl(PR_SCHED_CORE, PR_SCHED_CORE_SHARE_TO, 0, PIDTYPE_PGID, 0) < 0)
 		handle_error("core_sched share to self failed -- PGID");
 	disp_processes(num_processes, procs);
 
-	validate(get_cs_cookie(0) == get_cs_cookie(pid));
-	validate(get_cs_cookie(pid) != 0);
-	validate(get_cs_cookie(pid) == get_cs_cookie(procs[pidx].thr_tids[0]));
+	validate(get_cs_cookie_or_die(0) == get_cs_cookie_or_die(pid));
+	validate(get_cs_cookie_or_die(pid) != 0);
+	validate(get_cs_cookie_or_die(pid) ==
+		 get_cs_cookie_or_die(procs[pidx].thr_tids[0]));
 
 	validate(_prctl(PR_SCHED_CORE, PR_SCHED_CORE_MAX, 0, PIDTYPE_PGID, 0) < 0
 		&& errno == EINVAL);
-- 
2.55.0