From: Swapnil Sapkal <swapnil.sapkal@amd.com>
Date: Wed, 20 May 2026 10:20:16 +0000 (+0000)
Subject: perf sched stats: Fix SIGCHLD vs pause() race in schedstat_live()
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5b8c90e06622308ff4b6c14260baee6fad064289;p=thirdparty%2Flinux.git

perf sched stats: Fix SIGCHLD vs pause() race in schedstat_live()

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: replace pause() with a loop checking the 'done'
flag and using waitpid(WNOHANG) for the workload case.

Suggested-by: Namhyung Kim <namhyung@kernel.org>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Swapnil Sapkal <swapnil.sapkal@amd.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 4f54a08e66728..812a1b0d56d6e 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -4743,6 +4743,7 @@ static int perf_sched__schedstat_live(struct perf_sched *sched,
 	int reset = 0;
 	int err = 0;
 
+	done = 0;
 	signal(SIGINT, sighandler);
 	signal(SIGCHLD, sighandler);
 	signal(SIGTERM, sighandler);
@@ -4788,8 +4789,11 @@ static int perf_sched__schedstat_live(struct perf_sched *sched,
 	if (argc)
 		evlist__start_workload(evlist);
 
-	/* wait for signal */
-	pause();
+	while (!done) {
+		if (argc && waitpid(evlist->workload.pid, NULL, WNOHANG) > 0)
+			break;
+		sleep(1);
+	}
 
 	if (reset) {
 		err = disable_sched_schedstat();