selftests/perf_events: Test FASYNC with watermark wakeups

The test uses PERF_RECORD_SWITCH records to fill the ring buffer and
trigger the watermark wakeup, which in turn should trigger an IO
signal.

Signed-off-by: Kyle Huey <khuey@kylehuey.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240413141618.4160-4-khuey@kylehuey.com

tools/testing/selftests/perf_events/.gitignore

@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
 sigtrap_threads
 remove_on_exec
+watermark_signal

tools/testing/selftests/perf_events/Makefile

@@ -2,5 +2,5 @@
 CFLAGS += -Wl,-no-as-needed -Wall $(KHDR_INCLUDES)
 LDFLAGS += -lpthread
 
-TEST_GEN_PROGS := sigtrap_threads remove_on_exec
+TEST_GEN_PROGS := sigtrap_threads remove_on_exec watermark_signal
 include ../lib.mk

tools/testing/selftests/perf_events/watermark_signal.c

@@ -0,0 +1,146 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/perf_event.h>
+#include <stddef.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "../kselftest_harness.h"
+
+#define __maybe_unused __attribute__((__unused__))
+
+static int sigio_count;
+
+static void handle_sigio(int signum __maybe_unused,
+			 siginfo_t *oh __maybe_unused,
+			 void *uc __maybe_unused)
+{
+	++sigio_count;
+}
+
+static void do_child(void)
+{
+	raise(SIGSTOP);
+
+	for (int i = 0; i < 20; ++i)
+		sleep(1);
+
+	raise(SIGSTOP);
+
+	exit(0);
+}
+
+TEST(watermark_signal)
+{
+	struct perf_event_attr attr;
+	struct perf_event_mmap_page *p = NULL;
+	struct sigaction previous_sigio, sigio = { 0 };
+	pid_t child = -1;
+	int child_status;
+	int fd = -1;
+	long page_size = sysconf(_SC_PAGE_SIZE);
+
+	sigio.sa_sigaction = handle_sigio;
+	EXPECT_EQ(sigaction(SIGIO, &sigio, &previous_sigio), 0);
+
+	memset(&attr, 0, sizeof(attr));
+	attr.size = sizeof(attr);
+	attr.type = PERF_TYPE_SOFTWARE;
+	attr.config = PERF_COUNT_SW_DUMMY;
+	attr.sample_period = 1;
+	attr.disabled = 1;
+	attr.watermark = 1;
+	attr.context_switch = 1;
+	attr.wakeup_watermark = 1;
+
+	child = fork();
+	EXPECT_GE(child, 0);
+	if (child == 0)
+		do_child();
+	else if (child < 0) {
+		perror("fork()");
+		goto cleanup;
+	}
+
+	if (waitpid(child, &child_status, WSTOPPED) != child ||
+	    !(WIFSTOPPED(child_status) && WSTOPSIG(child_status) == SIGSTOP)) {
+		fprintf(stderr,
+			"failed to sycnhronize with child errno=%d status=%x\n",
+			errno,
+			child_status);
+		goto cleanup;
+	}
+
+	fd = syscall(__NR_perf_event_open, &attr, child, -1, -1,
+		     PERF_FLAG_FD_CLOEXEC);
+	if (fd < 0) {
+		fprintf(stderr, "failed opening event %llx\n", attr.config);
+		goto cleanup;
+	}
+
+	if (fcntl(fd, F_SETFL, FASYNC)) {
+		perror("F_SETFL FASYNC");
+		goto cleanup;
+	}
+
+	if (fcntl(fd, F_SETOWN, getpid())) {
+		perror("F_SETOWN getpid()");
+		goto cleanup;
+	}
+
+	if (fcntl(fd, F_SETSIG, SIGIO)) {
+		perror("F_SETSIG SIGIO");
+		goto cleanup;
+	}
+
+	p = mmap(NULL, 2 * page_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	if (p == NULL) {
+		perror("mmap");
+		goto cleanup;
+	}
+
+	if (ioctl(fd, PERF_EVENT_IOC_ENABLE, 0)) {
+		perror("PERF_EVENT_IOC_ENABLE");
+		goto cleanup;
+	}
+
+	if (kill(child, SIGCONT) < 0) {
+		perror("SIGCONT");
+		goto cleanup;
+	}
+
+	if (waitpid(child, &child_status, WSTOPPED) != -1 || errno != EINTR)
+		fprintf(stderr,
+			"expected SIGIO to terminate wait errno=%d status=%x\n%d",
+			errno,
+			child_status,
+			sigio_count);
+
+	EXPECT_GE(sigio_count, 1);
+
+cleanup:
+	if (p != NULL)
+		munmap(p, 2 * page_size);
+
+	if (fd >= 0)
+		close(fd);
+
+	if (child > 0) {
+		kill(child, SIGKILL);
+		waitpid(child, NULL, 0);
+	}
+
+	sigaction(SIGIO, &previous_sigio, NULL);
+}
+
+TEST_HARNESS_MAIN