[PATCH v3 2/3] perf sched stats: Fix SIGCHLD vs pause() race in schedstat_live()

[Swapnil Sapkal <swapnil.sapkal@amd.com>]

perf_sched__schedstat_live() has the same lost-wakeup race as
perf_sched__schedstat_record(): a short-lived workload's SIGCHLD
can be consumed by the signal handler before pause() is entered,
hanging the process.

Apply the same fix: use waitpid() for workload mode and
'while (!done) sleep(1)' for system-wide mode.

Suggested-by: Namhyung Kim <namhyung@kernel.org>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Swapnil Sapkal <swapnil.sapkal@amd.com>
---
 tools/perf/builtin-sched.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index cfd93bf11c2e..36fbc20dbebd 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -4695,11 +4695,15 @@ static int perf_sched__schedstat_live(struct perf_sched *sched,
 	if (err < 0)
 		goto out;
 
-	if (argc)
-		evlist__start_workload(evlist);
+	done = 0;
 
-	/* wait for signal */
-	pause();
+	if (argc) {
+		evlist__start_workload(evlist);
+		waitpid(evlist->workload.pid, NULL, 0);
+	} else {
+		while (!done)
+			sleep(1);
+	}
 
 	if (reset) {
 		err = disable_sched_schedstat();
-- 
2.43.0