monitor_timerfn(), lowpri_timerfn() and round_robin_timerfn() ignore
bpf_timer_start()'s return value: a failed re-arm silently stops the
periodic heartbeat, starving every task parked in LOWPRI_DSQ (lowpri)
or freezing cid rotation (round-robin).  Check the returns and raise
scx_bpf_error(), matching the init paths.

Signed-off-by: Wanwu Li <liwanwu@kylinos.cn>
---
 tools/sched_ext/scx_qmap.bpf.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c
index 5bb8b90a275a..9f6e61d7ca07 100644
--- a/tools/sched_ext/scx_qmap.bpf.c
+++ b/tools/sched_ext/scx_qmap.bpf.c
@@ -1246,7 +1246,8 @@ static int monitor_timerfn(void *map, int *key, struct bpf_timer *timer)
 			   scx_read_event(&events, SCX_EV_BYPASS_ACTIVATE));
 	}
 
-	bpf_timer_start(timer, ONE_SEC_IN_NS, 0);
+	if (bpf_timer_start(timer, ONE_SEC_IN_NS, 0))
+		scx_bpf_error("failed to re-arm stats timer");
 	return 0;
 }
 
@@ -1268,7 +1269,8 @@ struct {
 static int lowpri_timerfn(void *map, int *key, struct bpf_timer *timer)
 {
 	scx_bpf_dsq_reenq(LOWPRI_DSQ, 0);
-	bpf_timer_start(timer, LOWPRI_INTV_NS, 0);
+	if (bpf_timer_start(timer, LOWPRI_INTV_NS, 0))
+		scx_bpf_error("failed to re-arm lowpri timer");
 	return 0;
 }
 
@@ -1747,7 +1749,8 @@ static void rr_advance(void)
 static int round_robin_timerfn(void *map, int *key, struct bpf_timer *timer)
 {
 	rr_advance();
-	bpf_timer_start(timer, round_robin_ns, 0);
+	if (bpf_timer_start(timer, round_robin_ns, 0))
+		scx_bpf_error("failed to re-arm round-robin timer");
 	return 0;
 }
 
-- 
2.25.1