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, 47 insertions, 0 deletions

diff --git a/drivers/perf/arm_brbe.h b/drivers/perf/arm_brbe.h
new file mode 100644
index 000000000..b7c7d8796
--- /dev/null
+++ b/drivers/perf/arm_brbe.h
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Branch Record Buffer Extension Helpers.
+ *
+ * Copyright (C) 2022-2025 ARM Limited
+ *
+ * Author: Anshuman Khandual <anshuman.khandual@arm.com>
+ */
+
+struct arm_pmu;
+struct perf_branch_stack;
+struct perf_event;
+
+#ifdef CONFIG_ARM64_BRBE
+void brbe_probe(struct arm_pmu *arm_pmu);
+unsigned int brbe_num_branch_records(const struct arm_pmu *armpmu);
+void brbe_invalidate(void);
+
+void brbe_enable(const struct arm_pmu *arm_pmu);
+void brbe_disable(void);
+
+bool brbe_branch_attr_valid(struct perf_event *event);
+void brbe_read_filtered_entries(struct perf_branch_stack *branch_stack,
+				const struct perf_event *event);
+#else
+static inline void brbe_probe(struct arm_pmu *arm_pmu) { }
+static inline unsigned int brbe_num_branch_records(const struct arm_pmu *armpmu)
+{
+	return 0;
+}
+
+static inline void brbe_invalidate(void) { }
+
+static inline void brbe_enable(const struct arm_pmu *arm_pmu) { };
+static inline void brbe_disable(void) { };
+
+static inline bool brbe_branch_attr_valid(struct perf_event *event)
+{
+	WARN_ON_ONCE(!has_branch_stack(event));
+	return false;
+}
+
+static void brbe_read_filtered_entries(struct perf_branch_stack *branch_stack,
+				       const struct perf_event *event)
+{
+}
+#endif