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, 104 insertions, 0 deletions

diff --git a/tools/perf/util/unwind.c b/tools/perf/util/unwind.c
new file mode 100644
index 000000000..4ed4b1d55
--- /dev/null
+++ b/tools/perf/util/unwind.c
@@ -0,0 +1,104 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "debug.h"
+#include "symbol_conf.h"
+#include "unwind.h"
+#include <linux/string.h>
+#include <string.h>
+#include <stdlib.h>
+
+int unwind__get_entries(unwind_entry_cb_t cb __maybe_unused, void *arg __maybe_unused,
+			struct thread *thread __maybe_unused,
+			struct perf_sample *data __maybe_unused,
+			int max_stack __maybe_unused,
+			bool best_effort __maybe_unused)
+{
+	int ret = 0;
+
+#if defined(HAVE_LIBDW_SUPPORT) || defined(HAVE_LIBUNWIND_SUPPORT)
+	if (symbol_conf.unwind_style[0] == UNWIND_STYLE_UNKNOWN) {
+		int i = 0;
+#ifdef HAVE_LIBDW_SUPPORT
+		symbol_conf.unwind_style[i++] = UNWIND_STYLE_LIBDW;
+#endif
+#ifdef HAVE_LIBUNWIND_SUPPORT
+		symbol_conf.unwind_style[i++] = UNWIND_STYLE_LIBUNWIND;
+#endif
+	}
+#endif //defined(HAVE_LIBDW_SUPPORT) || defined(HAVE_LIBUNWIND_SUPPORT)
+
+	for (size_t i = 0; i < ARRAY_SIZE(symbol_conf.unwind_style); i++) {
+		switch (symbol_conf.unwind_style[i]) {
+		case UNWIND_STYLE_LIBDW:
+			ret = libdw__get_entries(cb, arg, thread, data, max_stack, best_effort);
+			break;
+		case UNWIND_STYLE_LIBUNWIND:
+			ret = libunwind__get_entries(cb, arg, thread, data, max_stack, best_effort);
+			break;
+		case UNWIND_STYLE_UNKNOWN:
+		default:
+#if !defined(HAVE_LIBDW_SUPPORT) && !defined(HAVE_LIBUNWIND_SUPPORT)
+			pr_warning_once(
+				"Error: dwarf unwinding not supported, build perf with libdw or libunwind.\n");
+#endif
+			ret = 0;
+			break;
+		}
+		if (ret > 0) {
+			ret = 0;
+			break;
+		}
+		if (ret < 0)
+			break;
+	}
+	return ret;
+}
+
+int unwind__configure(const char *var, const char *value, void *cb __maybe_unused)
+{
+	static const char * const unwind_style_names[] = {
+		[UNWIND_STYLE_LIBDW] = "libdw",
+		[UNWIND_STYLE_LIBUNWIND] = "libunwind",
+		NULL
+	};
+	char *s, *p, *saveptr;
+	size_t i = 0;
+
+	if (strcmp(var, "unwind.style"))
+		return 0;
+
+	if (!value)
+		return -1;
+
+	s = strdup(value);
+	if (!s)
+		return -1;
+
+	memset(symbol_conf.unwind_style, 0, sizeof(symbol_conf.unwind_style));
+
+	p = strtok_r(s, ",", &saveptr);
+	while (p && i < ARRAY_SIZE(symbol_conf.unwind_style)) {
+		bool found = false;
+		char *q = strim(p);
+
+		for (size_t j = UNWIND_STYLE_LIBDW; j < MAX_UNWIND_STYLE; j++) {
+			if (!strcasecmp(q, unwind_style_names[j])) {
+				symbol_conf.unwind_style[i++] = j;
+				found = true;
+				break;
+			}
+		}
+		if (!found)
+			pr_warning("Unknown unwind style: %s\n", q);
+		p = strtok_r(NULL, ",", &saveptr);
+	}
+
+	free(s);
+	return 0;
+}
+
+int unwind__option(const struct option *opt __maybe_unused,
+		   const char *arg,
+		   int unset __maybe_unused)
+{
+	return unwind__configure("unwind.style", arg, NULL);
+}