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, 85 insertions, 0 deletions

diff --git a/tools/perf/util/unwind.h b/tools/perf/util/unwind.h
new file mode 100644
index 000000000..a2d4af694
--- /dev/null
+++ b/tools/perf/util/unwind.h
@@ -0,0 +1,85 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UNWIND_H
+#define __UNWIND_H
+
+#include <stdint.h>
+#include <linux/compiler.h>
+#include <linux/types.h>
+#include "map_symbol.h"
+
+struct maps;
+struct option;
+struct perf_sample;
+struct thread;
+
+struct unwind_entry {
+	struct map_symbol ms;
+	u64		  ip;
+};
+
+typedef int (*unwind_entry_cb_t)(struct unwind_entry *entry, void *arg);
+
+int unwind__configure(const char *var, const char *value, void *cb);
+int unwind__option(const struct option *opt, const char *arg, int unset);
+
+/*
+ * When best_effort is set, don't report errors and fail silently. This could
+ * be expanded in the future to be more permissive about things other than
+ * error messages.
+ */
+int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
+			struct thread *thread,
+			struct perf_sample *data, int max_stack,
+			bool best_effort);
+
+#ifdef HAVE_LIBDW_SUPPORT
+int libdw__get_entries(unwind_entry_cb_t cb, void *arg,
+		       struct thread *thread,
+		       struct perf_sample *data, int max_stack,
+		       bool best_effort);
+#else
+#include "debug.h"
+static inline int libdw__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)
+{
+	pr_warning_once("Error: libdw dwarf unwinding not built into perf\n");
+	return 0;
+}
+#endif
+
+#ifdef HAVE_LIBUNWIND_SUPPORT
+/* libunwind specific */
+int libunwind__get_entries(unwind_entry_cb_t cb, void *arg,
+			   struct thread *thread,
+			   struct perf_sample *data, int max_stack,
+			   bool best_effort);
+int unwind__prepare_access(struct maps *maps, uint16_t e_machine);
+void unwind__flush_access(struct maps *maps);
+void unwind__finish_access(struct maps *maps);
+#else
+#include "debug.h"
+static inline int libunwind__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)
+{
+	pr_warning_once("Error: libunwind dwarf unwinding not built into perf\n");
+	return 0;
+}
+
+static inline int unwind__prepare_access(struct maps *maps __maybe_unused,
+					 uint16_t e_machine __maybe_unused)
+{
+	return 0;
+}
+
+static inline void unwind__flush_access(struct maps *maps __maybe_unused) {}
+static inline void unwind__finish_access(struct maps *maps __maybe_unused) {}
+#endif
+
+#endif /* __UNWIND_H */