ftrace: Switch ftrace.c code over to use guard()

There are a few functions in ftrace.c that have "goto out" or equivalent
on error in order to release locks that were taken. This can be error
prone or just simply make the code more complex.

Switch every location that ends with unlocking a mutex on error over to
using the guard(mutex)() infrastructure to let the compiler worry about
releasing locks. This makes the code easier to read and understand.

Cc: Masami Hiramatsu <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Mathieu Desnoyers <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Link: https://lore.kernel.org/[e-mail]
Signed-off-by: Steven Rostedt (Google) <[e-mail]>

kernel/trace/ftrace.c

···
 {
 	struct ftrace_profile *rec = v;
 	char str[KSYM_SYMBOL_LEN];
-	int ret = 0;
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	static struct trace_seq s;
 	unsigned long long avg;
 	unsigned long long stddev;
 #endif
-	mutex_lock(&ftrace_profile_lock);
+	guard(mutex)(&ftrace_profile_lock);
 
 	/* we raced with function_profile_reset() */
-	if (unlikely(rec->counter == 0)) {
-		ret = -EBUSY;
-		goto out;
-	}
+	if (unlikely(rec->counter == 0))
+		return -EBUSY;
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	avg = div64_ul(rec->time, rec->counter);
 	if (tracing_thresh && (avg < tracing_thresh))
-		goto out;
+		return 0;
 #endif
 
 	kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
···
 	trace_print_seq(m, &s);
 #endif
 	seq_putc(m, '\n');
-out:
-	mutex_unlock(&ftrace_profile_lock);
 
-	return ret;
+	return 0;
 }
 
 static void ftrace_profile_reset(struct ftrace_profile_stat *stat)
···
 
 	val = !!val;
 
-	mutex_lock(&ftrace_profile_lock);
+	guard(mutex)(&ftrace_profile_lock);
 	if (ftrace_profile_enabled ^ val) {
 		if (val) {
 			ret = ftrace_profile_init();
-			if (ret < 0) {
-				cnt = ret;
-				goto out;
-			}
+			if (ret < 0)
+				return ret;
 
 			ret = register_ftrace_profiler();
-			if (ret < 0) {
-				cnt = ret;
-				goto out;
-			}
+			if (ret < 0)
+				return ret;
 			ftrace_profile_enabled = 1;
 		} else {
 			ftrace_profile_enabled = 0;
···
 			unregister_ftrace_profiler();
 		}
 	}
- out:
-	mutex_unlock(&ftrace_profile_lock);
 
 	*ppos += cnt;
 
···
 __init int register_ftrace_command(struct ftrace_func_command *cmd)
 {
 	struct ftrace_func_command *p;
-	int ret = 0;
 
-	mutex_lock(&ftrace_cmd_mutex);
+	guard(mutex)(&ftrace_cmd_mutex);
 	list_for_each_entry(p, &ftrace_commands, list) {
-		if (strcmp(cmd->name, p->name) == 0) {
-			ret = -EBUSY;
-			goto out_unlock;
-		}
+		if (strcmp(cmd->name, p->name) == 0)
+			return -EBUSY;
 	}
 	list_add(&cmd->list, &ftrace_commands);
- out_unlock:
-	mutex_unlock(&ftrace_cmd_mutex);
 
-	return ret;
+	return 0;
 }
 
 /*
···
 __init int unregister_ftrace_command(struct ftrace_func_command *cmd)
 {
 	struct ftrace_func_command *p, *n;
-	int ret = -ENODEV;
 
-	mutex_lock(&ftrace_cmd_mutex);
+	guard(mutex)(&ftrace_cmd_mutex);
+
 	list_for_each_entry_safe(p, n, &ftrace_commands, list) {
 		if (strcmp(cmd->name, p->name) == 0) {
-			ret = 0;
 			list_del_init(&p->list);
-			goto out_unlock;
+			return 0;
 		}
 	}
- out_unlock:
-	mutex_unlock(&ftrace_cmd_mutex);
 
-	return ret;
+	return -ENODEV;
 }
 
 static int ftrace_process_regex(struct ftrace_iterator *iter,
···
 	struct trace_array *tr = iter->ops->private;
 	char *func, *command, *next = buff;
 	struct ftrace_func_command *p;
-	int ret = -EINVAL;
+	int ret;
 
 	func = strsep(&next, ":");
 
···
 
 	command = strsep(&next, ":");
 
-	mutex_lock(&ftrace_cmd_mutex);
-	list_for_each_entry(p, &ftrace_commands, list) {
-		if (strcmp(p->name, command) == 0) {
-			ret = p->func(tr, hash, func, command, next, enable);
-			goto out_unlock;
-		}
-	}
- out_unlock:
-	mutex_unlock(&ftrace_cmd_mutex);
+	guard(mutex)(&ftrace_cmd_mutex);
 
-	return ret;
+	list_for_each_entry(p, &ftrace_commands, list) {
+		if (strcmp(p->name, command) == 0)
+			return p->func(tr, hash, func, command, next, enable);
+	}
+
+	return -EINVAL;
 }
 
 static ssize_t
···
 	if (!cnt)
 		return 0;
 
-	mutex_lock(&ftrace_lock);
+	guard(mutex)(&ftrace_lock);
 
 	switch (type) {
 	case TRACE_PIDS:
···
 					     lockdep_is_held(&ftrace_lock));
 		break;
 	default:
-		ret = -EINVAL;
 		WARN_ON_ONCE(1);
-		goto out;
+		return -EINVAL;
 	}
 
 	ret = trace_pid_write(filtered_pids, &pid_list, ubuf, cnt);
 	if (ret < 0)
-		goto out;
+		return ret;
 
 	switch (type) {
 	case TRACE_PIDS:
···
 
 	ftrace_update_pid_func();
 	ftrace_startup_all(0);
- out:
-	mutex_unlock(&ftrace_lock);
 
-	if (ret > 0)
-		*ppos += ret;
+	*ppos += ret;
 
 	return ret;
 }
···
 ftrace_enable_sysctl(const struct ctl_table *table, int write,
 		     void *buffer, size_t *lenp, loff_t *ppos)
 {
-	int ret = -ENODEV;
+	int ret;
 
-	mutex_lock(&ftrace_lock);
+	guard(mutex)(&ftrace_lock);
 
 	if (unlikely(ftrace_disabled))
-		goto out;
+		return -ENODEV;
 
 	ret = proc_dointvec(table, write, buffer, lenp, ppos);
 
 	if (ret || !write || (last_ftrace_enabled == !!ftrace_enabled))
-		goto out;
+		return ret;
 
 	if (ftrace_enabled) {
 
···
 	} else {
 		if (is_permanent_ops_registered()) {
 			ftrace_enabled = true;
-			ret = -EBUSY;
-			goto out;
+			return -EBUSY;
 		}
 
 		/* stopping ftrace calls (just send to ftrace_stub) */
···
 	}
 
 	last_ftrace_enabled = !!ftrace_enabled;
- out:
-	mutex_unlock(&ftrace_lock);
-	return ret;
+	return 0;
 }
 
 static struct ctl_table ftrace_sysctls[] = {