ftrace: Add modify_ftrace_direct_multi_nolock

This is similar to modify_ftrace_direct_multi, but does not acquire
direct_mutex. This is useful when direct_mutex is already locked by the
user.
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/bpf/20220720002126.803253-2-song@kernel.org

include/linux/ftrace.h

@@ -340,6 +340,7 @@ unsigned long ftrace_find_rec_direct(unsigned long ip);
 int register_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr);
 int unregister_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr);
 int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr);
+int modify_ftrace_direct_multi_nolock(struct ftrace_ops *ops, unsigned long addr);
 
 #else
 struct ftrace_ops;
@@ -384,6 +385,10 @@ static inline int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned lo
 {
 	return -ENODEV;
 }
+static inline int modify_ftrace_direct_multi_nolock(struct ftrace_ops *ops, unsigned long addr)
+{
+	return -ENODEV;
+}
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
 
 #ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS

kernel/trace/ftrace.c

@@ -5691,22 +5691,8 @@ int unregister_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr)
 }
 EXPORT_SYMBOL_GPL(unregister_ftrace_direct_multi);
 
-/**
- * modify_ftrace_direct_multi - Modify an existing direct 'multi' call
- * to call something else
- * @ops: The address of the struct ftrace_ops object
- * @addr: The address of the new trampoline to call at @ops functions
- *
- * This is used to unregister currently registered direct caller and
- * register new one @addr on functions registered in @ops object.
- *
- * Note there's window between ftrace_shutdown and ftrace_startup calls
- * where there will be no callbacks called.
- *
- * Returns: zero on success. Non zero on error, which includes:
- *  -EINVAL - The @ops object was not properly registered.
- */
-int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr)
+static int
+__modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr)
 {
 	struct ftrace_hash *hash;
 	struct ftrace_func_entry *entry, *iter;
@@ -5717,12 +5703,7 @@ int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr)
 	int i, size;
 	int err;
 
-	if (check_direct_multi(ops))
-		return -EINVAL;
-	if (!(ops->flags & FTRACE_OPS_FL_ENABLED))
-		return -EINVAL;
-
-	mutex_lock(&direct_mutex);
+	lockdep_assert_held_once(&direct_mutex);
 
 	/* Enable the tmp_ops to have the same functions as the direct ops */
 	ftrace_ops_init(&tmp_ops);
@@ -5730,7 +5711,7 @@ int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr)
 
 	err = register_ftrace_function(&tmp_ops);
 	if (err)
-		goto out_direct;
+		return err;
 
 	/*
 	 * Now the ftrace_ops_list_func() is called to do the direct callers.
@@ -5754,7 +5735,64 @@ int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr)
 	/* Removing the tmp_ops will add the updated direct callers to the functions */
 	unregister_ftrace_function(&tmp_ops);
 
- out_direct:
+	return err;
+}
+
+/**
+ * modify_ftrace_direct_multi_nolock - Modify an existing direct 'multi' call
+ * to call something else
+ * @ops: The address of the struct ftrace_ops object
+ * @addr: The address of the new trampoline to call at @ops functions
+ *
+ * This is used to unregister currently registered direct caller and
+ * register new one @addr on functions registered in @ops object.
+ *
+ * Note there's window between ftrace_shutdown and ftrace_startup calls
+ * where there will be no callbacks called.
+ *
+ * Caller should already have direct_mutex locked, so we don't lock
+ * direct_mutex here.
+ *
+ * Returns: zero on success. Non zero on error, which includes:
+ *  -EINVAL - The @ops object was not properly registered.
+ */
+int modify_ftrace_direct_multi_nolock(struct ftrace_ops *ops, unsigned long addr)
+{
+	if (check_direct_multi(ops))
+		return -EINVAL;
+	if (!(ops->flags & FTRACE_OPS_FL_ENABLED))
+		return -EINVAL;
+
+	return __modify_ftrace_direct_multi(ops, addr);
+}
+EXPORT_SYMBOL_GPL(modify_ftrace_direct_multi_nolock);
+
+/**
+ * modify_ftrace_direct_multi - Modify an existing direct 'multi' call
+ * to call something else
+ * @ops: The address of the struct ftrace_ops object
+ * @addr: The address of the new trampoline to call at @ops functions
+ *
+ * This is used to unregister currently registered direct caller and
+ * register new one @addr on functions registered in @ops object.
+ *
+ * Note there's window between ftrace_shutdown and ftrace_startup calls
+ * where there will be no callbacks called.
+ *
+ * Returns: zero on success. Non zero on error, which includes:
+ *  -EINVAL - The @ops object was not properly registered.
+ */
+int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr)
+{
+	int err;
+
+	if (check_direct_multi(ops))
+		return -EINVAL;
+	if (!(ops->flags & FTRACE_OPS_FL_ENABLED))
+		return -EINVAL;
+
+	mutex_lock(&direct_mutex);
+	err = __modify_ftrace_direct_multi(ops, addr);
 	mutex_unlock(&direct_mutex);
 	return err;
 }