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, 118 insertions, 0 deletions

diff --git a/tools/lib/perf/threadmap.c b/tools/lib/perf/threadmap.c
new file mode 100644
index 000000000..db431b036
--- /dev/null
+++ b/tools/lib/perf/threadmap.c
@@ -0,0 +1,118 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <perf/threadmap.h>
+#include <stdlib.h>
+#include <linux/refcount.h>
+#include <internal/threadmap.h>
+#include <string.h>
+#include <asm/bug.h>
+#include <stdio.h>
+
+static void perf_thread_map__reset(struct perf_thread_map *map, int start, int nr)
+{
+	size_t size = (nr - start) * sizeof(map->map[0]);
+
+	memset(&map->map[start], 0, size);
+	map->err_thread = -1;
+}
+
+struct perf_thread_map *perf_thread_map__realloc(struct perf_thread_map *map, int nr)
+{
+	size_t size = sizeof(*map) + sizeof(map->map[0]) * nr;
+	int start = map ? map->nr : 0;
+
+	map = realloc(map, size);
+	/*
+	 * We only realloc to add more items, let's reset new items.
+	 */
+	if (map)
+		perf_thread_map__reset(map, start, nr);
+
+	return map;
+}
+
+#define thread_map__alloc(__nr) perf_thread_map__realloc(NULL, __nr)
+
+void perf_thread_map__set_pid(struct perf_thread_map *map, int idx, pid_t pid)
+{
+	map->map[idx].pid = pid;
+}
+
+char *perf_thread_map__comm(struct perf_thread_map *map, int idx)
+{
+	return map->map[idx].comm;
+}
+
+struct perf_thread_map *perf_thread_map__new_array(int nr_threads, pid_t *array)
+{
+	struct perf_thread_map *threads = thread_map__alloc(nr_threads);
+	int i;
+
+	if (!threads)
+		return NULL;
+
+	for (i = 0; i < nr_threads; i++)
+		perf_thread_map__set_pid(threads, i, array ? array[i] : -1);
+
+	threads->nr = nr_threads;
+	refcount_set(&threads->refcnt, 1);
+
+	return threads;
+}
+
+struct perf_thread_map *perf_thread_map__new_dummy(void)
+{
+	return perf_thread_map__new_array(1, NULL);
+}
+
+static void perf_thread_map__delete(struct perf_thread_map *threads)
+{
+	if (threads) {
+		int i;
+
+		WARN_ONCE(refcount_read(&threads->refcnt) != 0,
+			  "thread map refcnt unbalanced\n");
+		for (i = 0; i < threads->nr; i++)
+			free(perf_thread_map__comm(threads, i));
+		free(threads);
+	}
+}
+
+struct perf_thread_map *perf_thread_map__get(struct perf_thread_map *map)
+{
+	if (map)
+		refcount_inc(&map->refcnt);
+	return map;
+}
+
+void perf_thread_map__put(struct perf_thread_map *map)
+{
+	if (map && refcount_dec_and_test(&map->refcnt))
+		perf_thread_map__delete(map);
+}
+
+int perf_thread_map__nr(struct perf_thread_map *threads)
+{
+	return threads ? threads->nr : 1;
+}
+
+pid_t perf_thread_map__pid(struct perf_thread_map *map, int idx)
+{
+	if (!map) {
+		assert(idx == 0);
+		return -1;
+	}
+
+	return map->map[idx].pid;
+}
+
+int perf_thread_map__idx(struct perf_thread_map *threads, pid_t pid)
+{
+	if (!threads)
+		return pid == -1 ? 0 : -1;
+
+	for (int i = 0; i < threads->nr; ++i) {
+		if (threads->map[i].pid == pid)
+			return i;
+	}
+	return -1;
+}