From: Swapnil Sapkal <swapnil.sapkal@amd.com>
Date: Wed, 20 May 2026 10:20:17 +0000 (+0000)
Subject: perf lock contention: Fix SIGCHLD vs pause() race in __cmd_contention()
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=35c9fb22000f1ce10c0f3627d30fa8763e721719;p=thirdparty%2Fkernel%2Fstable.git

perf lock contention: Fix SIGCHLD vs pause() race in __cmd_contention()

__cmd_contention() suffers from the same lost-wakeup race as the perf
sched stats paths: 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-lock.c b/tools/perf/builtin-lock.c
index 064b3aa4bad7..94a8c35abb0b 100644
--- a/tools/perf/builtin-lock.c
+++ b/tools/perf/builtin-lock.c
@@ -31,6 +31,7 @@
 #include <stdio.h>
 #include <sys/types.h>
 #include <sys/prctl.h>
+#include <sys/wait.h>
 #include <semaphore.h>
 #include <math.h>
 #include <limits.h>
@@ -1915,8 +1916,11 @@ out_delete:
 	return err;
 }
 
+static volatile sig_atomic_t done;
+
 static void sighandler(int sig __maybe_unused)
 {
+	done = 1;
 }
 
 static int check_lock_contention_options(const struct option *options,
@@ -2054,6 +2058,7 @@ static int __cmd_contention(int argc, const char **argv)
 			goto out_delete;
 		}
 
+		done = 0;
 		signal(SIGINT, sighandler);
 		signal(SIGCHLD, sighandler);
 		signal(SIGTERM, sighandler);
@@ -2121,8 +2126,11 @@ static int __cmd_contention(int argc, const char **argv)
 		if (argc)
 			evlist__start_workload(con.evlist);
 
-		/* wait for signal */
-		pause();
+		while (!done) {
+			if (argc && waitpid(con.evlist->workload.pid, NULL, WNOHANG) > 0)
+				break;
+			sleep(1);
+		}
 
 		lock_contention_stop();
 		lock_contention_read(&con);