tools/sched_ext: Don't restart over a pending exit request

The tools restart when the kernel exits the scheduler with
SCX_ECODE_ACT_RESTART. The restart decision doesn't consult exit_req, so an
exit request arriving while the restart condition persists is ignored and
the tool reloads in a tight loop. Test exit_req before restarting.

scx_userland needs more: its main loop never watches the kernel-side exit
and exit_req doubles as the stats printer's stop signal, set by the teardown
and reset on each restart. Add the missing UEI_EXITED() test and give the
printer its own stop flag so that exit_req only means an exit request and
stays latched like in the other tools.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

tools/sched_ext/scx_central.c

@@ -120,7 +120,7 @@ restart:
 	ecode = UEI_REPORT(skel, uei);
 	scx_central__destroy(skel);
 
-	if (UEI_ECODE_RESTART(ecode))
+	if (!exit_req && UEI_ECODE_RESTART(ecode))
 		goto restart;
 	return 0;
 }

tools/sched_ext/scx_cpu0.c

@@ -99,7 +99,7 @@ restart:
 	ecode = UEI_REPORT(skel, uei);
 	scx_cpu0__destroy(skel);
 
-	if (UEI_ECODE_RESTART(ecode))
+	if (!exit_req && UEI_ECODE_RESTART(ecode))
 		goto restart;
 	return 0;
 }

tools/sched_ext/scx_flatcg.c

@@ -233,7 +233,7 @@ restart:
 	ecode = UEI_REPORT(skel, uei);
 	scx_flatcg__destroy(skel);
 
-	if (UEI_ECODE_RESTART(ecode))
+	if (!exit_req && UEI_ECODE_RESTART(ecode))
 		goto restart;
 	return 0;
 }

tools/sched_ext/scx_pair.c

@@ -190,7 +190,7 @@ restart:
 	ecode = UEI_REPORT(skel, uei);
 	scx_pair__destroy(skel);
 
-	if (UEI_ECODE_RESTART(ecode))
+	if (!exit_req && UEI_ECODE_RESTART(ecode))
 		goto restart;
 	return 0;
 }

tools/sched_ext/scx_qmap.c

@@ -465,7 +465,7 @@ restart:
 	ecode = UEI_REPORT(skel, uei);
 	scx_qmap__destroy(skel);
 
-	if (UEI_ECODE_RESTART(ecode))
+	if (!exit_req && UEI_ECODE_RESTART(ecode))
 		goto restart;
 	return 0;
 }

tools/sched_ext/scx_sdt.c

@@ -96,7 +96,7 @@ restart:
 	ecode = UEI_REPORT(skel, uei);
 	scx_sdt__destroy(skel);
 
-	if (UEI_ECODE_RESTART(ecode))
+	if (!exit_req && UEI_ECODE_RESTART(ecode))
 		goto restart;
 	return 0;
 }

tools/sched_ext/scx_simple.c

@@ -104,7 +104,7 @@ restart:
 	ecode = UEI_REPORT(skel, uei);
 	scx_simple__destroy(skel);
 
-	if (UEI_ECODE_RESTART(ecode))
+	if (!exit_req && UEI_ECODE_RESTART(ecode))
 		goto restart;
 	return 0;
 }

tools/sched_ext/scx_userland.c

@@ -52,6 +52,7 @@ static __u32 batch_size = 8;
 
 static bool verbose;
 static volatile int exit_req;
+static volatile int stats_stop;
 static int enqueued_fd, dispatched_fd;
 
 static pthread_t stats_printer;
@@ -286,7 +287,7 @@ static void dispatch_batch(void)
 
 static void *run_stats_printer(void *arg)
 {
-	while (!exit_req) {
+	while (!stats_stop) {
 		__u64 nr_failed_enqueues, nr_kernel_enqueues, nr_user_enqueues, total;
 
 		nr_failed_enqueues = skel->bss->nr_failed_enqueues;
@@ -374,7 +375,7 @@ static void pre_bootstrap(int argc, char **argv)
 
 static void bootstrap(char *comm)
 {
-	exit_req = 0;
+	stats_stop = 0;
 	min_vruntime = 0.0;
 	__atomic_store_n(&nr_vruntime_enqueues, 0, __ATOMIC_RELAXED);
 	__atomic_store_n(&nr_vruntime_dispatches, 0, __ATOMIC_RELAXED);
@@ -404,7 +405,7 @@ static void bootstrap(char *comm)
 
 static void sched_main_loop(void)
 {
-	while (!exit_req) {
+	while (!exit_req && !UEI_EXITED(skel, uei)) {
 		/*
 		 * Perform the following work in the main user space scheduler
 		 * loop:
@@ -434,13 +435,13 @@ restart:
 	bootstrap(argv[0]);
 	sched_main_loop();
 
-	exit_req = 1;
+	stats_stop = 1;
 	bpf_link__destroy(ops_link);
 	pthread_join(stats_printer, NULL);
 	ecode = UEI_REPORT(skel, uei);
 	scx_userland__destroy(skel);
 
-	if (UEI_ECODE_RESTART(ecode))
+	if (!exit_req && UEI_ECODE_RESTART(ecode))
 		goto restart;
 	return 0;
 }