ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 161 insertions, 0 deletions

diff --git a/tools/perf/tests/task-exit.c b/tools/perf/tests/task-exit.c
new file mode 100644
index 000000000..95393edbf
--- /dev/null
+++ b/tools/perf/tests/task-exit.c
@@ -0,0 +1,161 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "debug.h"
+#include "evlist.h"
+#include "evsel.h"
+#include "target.h"
+#include "thread_map.h"
+#include "tests.h"
+#include "util/mmap.h"
+
+#include <errno.h>
+#include <signal.h>
+#include <linux/string.h>
+#include <perf/cpumap.h>
+#include <perf/evlist.h>
+#include <perf/mmap.h>
+
+static int exited;
+static int nr_exit;
+
+static void sig_handler(int sig __maybe_unused)
+{
+	exited = 1;
+}
+
+/*
+ * evlist__prepare_workload will send a SIGUSR1 if the fork fails, since
+ * we asked by setting its exec_error to this handler.
+ */
+static void workload_exec_failed_signal(int signo __maybe_unused,
+					siginfo_t *info __maybe_unused,
+					void *ucontext __maybe_unused)
+{
+	exited	= 1;
+	nr_exit = -1;
+}
+
+/*
+ * This test will start a workload that does nothing then it checks
+ * if the number of exit event reported by the kernel is 1 or not
+ * in order to check the kernel returns correct number of event.
+ */
+static int test__task_exit(struct test_suite *test __maybe_unused, int subtest __maybe_unused)
+{
+	int err = -1;
+	union perf_event *event;
+	struct evsel *evsel;
+	struct evlist *evlist;
+	struct target target = {
+		.uses_mmap	= true,
+	};
+	const char *argv[] = { "true", NULL };
+	char sbuf[STRERR_BUFSIZE];
+	struct perf_cpu_map *cpus;
+	struct perf_thread_map *threads;
+	struct mmap *md;
+	int retry_count = 0;
+
+	signal(SIGCHLD, sig_handler);
+
+	evlist = evlist__new_dummy();
+	if (evlist == NULL) {
+		pr_debug("evlist__new_dummy\n");
+		return -1;
+	}
+
+	/*
+	 * Create maps of threads and cpus to monitor. In this case
+	 * we start with all threads and cpus (-1, -1) but then in
+	 * evlist__prepare_workload we'll fill in the only thread
+	 * we're monitoring, the one forked there.
+	 */
+	cpus = perf_cpu_map__new_any_cpu();
+	threads = thread_map__new_by_tid(-1);
+	if (!cpus || !threads) {
+		err = -ENOMEM;
+		pr_debug("Not enough memory to create thread/cpu maps\n");
+		goto out_put_evlist;
+	}
+
+	perf_evlist__set_maps(evlist__core(evlist), cpus, threads);
+
+	err = evlist__prepare_workload(evlist, &target, argv, false, workload_exec_failed_signal);
+	if (err < 0) {
+		pr_debug("Couldn't run the workload!\n");
+		goto out_put_evlist;
+	}
+
+	evsel = evlist__first(evlist);
+	evsel->core.attr.task = 1;
+#ifdef __s390x__
+	evsel->core.attr.sample_freq = 1000000;
+#else
+	evsel->core.attr.sample_freq = 1;
+#endif
+	evsel->core.attr.inherit = 0;
+	evsel->core.attr.watermark = 0;
+	evsel->core.attr.wakeup_events = 1;
+	evsel->core.attr.exclude_kernel = 1;
+
+	err = evlist__open(evlist);
+	if (err < 0) {
+		pr_debug("Couldn't open the evlist: %s\n",
+			 str_error_r(-err, sbuf, sizeof(sbuf)));
+		goto out_put_evlist;
+	}
+
+	if (evlist__do_mmap(evlist, 128) < 0) {
+		pr_debug("failed to mmap events: %d (%s)\n", errno,
+			 str_error_r(errno, sbuf, sizeof(sbuf)));
+		err = -1;
+		goto out_put_evlist;
+	}
+
+	evlist__start_workload(evlist);
+
+retry:
+	md = &evlist__mmap(evlist)[0];
+	if (perf_mmap__read_init(&md->core) < 0)
+		goto out_init;
+
+	while ((event = perf_mmap__read_event(&md->core)) != NULL) {
+		if (event->header.type == PERF_RECORD_EXIT)
+			nr_exit++;
+
+		perf_mmap__consume(&md->core);
+	}
+	perf_mmap__read_done(&md->core);
+
+out_init:
+	if (!exited || !nr_exit) {
+		evlist__poll(evlist, -1);
+
+		if (retry_count++ > 1000) {
+			pr_debug("Failed after retrying 1000 times\n");
+			err = -1;
+			goto out_put_evlist;
+		}
+
+		goto retry;
+	}
+
+	if (nr_exit != 1) {
+		pr_debug("received %d EXIT records\n", nr_exit);
+		err = -1;
+	}
+
+out_put_evlist:
+	perf_cpu_map__put(cpus);
+	perf_thread_map__put(threads);
+	evlist__put(evlist);
+	return err;
+}
+
+struct test_case tests__task_exit[] = {
+	TEST_CASE_EXCLUSIVE("Number of exit events of a simple workload", task_exit),
+	{	.name = NULL, }
+};
+struct test_suite suite__task_exit = {
+	.desc = "Number of exit events of a simple workload",
+	.test_cases = tests__task_exit,
+};