[PATCH v2 2/3] perf sched stats: Fix SIGCHLD race in schedstat_live()

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

The same signal race that exists in perf_sched__schedstat_record() also
affects perf_sched__schedstat_live(). A very short-lived workload can
exit and deliver SIGCHLD before pause() is entered, causing an
indefinite hang.

Apply the same fix: block SIGCHLD, SIGINT and SIGTERM after the
workload is forked (evlist__prepare_workload) but before it is started
(evlist__start_workload), then replace pause() with sigsuspend() to
atomically unblock and wait.

Reviewed-by: James Clark <james.clark@linaro.org>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Swapnil Sapkal <swapnil.sapkal@amd.com>
---
 tools/perf/builtin-sched.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 3f448acd5046..c716dd33a9c9 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -4653,6 +4653,7 @@ static int perf_sched__schedstat_live(struct perf_sched *sched,
 				      int argc, const char **argv)
 {
 	struct cpu_domain_map **cd_map = NULL;
+	sigset_t sig_mask, oldmask;
 	struct target target = {};
 	u32 __maybe_unused md;
 	struct evlist *evlist;
@@ -4702,11 +4703,17 @@ static int perf_sched__schedstat_live(struct perf_sched *sched,
 	if (err < 0)
 		goto out;
 
+	sigemptyset(&sig_mask);
+	sigaddset(&sig_mask, SIGCHLD);
+	sigaddset(&sig_mask, SIGINT);
+	sigaddset(&sig_mask, SIGTERM);
+	sigprocmask(SIG_BLOCK, &sig_mask, &oldmask);
+
 	if (argc)
 		evlist__start_workload(evlist);
 
-	/* wait for signal */
-	pause();
+	sigsuspend(&oldmask);
+	sigprocmask(SIG_SETMASK, &oldmask, NULL);
 
 	if (reset) {
 		err = disable_sched_schedstat();
-- 
2.43.0