tracing: Switch trace_events.c code over to use guard()

There are several functions in trace_events.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.

Some locations did some simple arithmetic after releasing the lock. As
this causes no real overhead for holding a mutex while processing the file
position (*ppos += cnt;) let the lock be held over this logic too.

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

Author: rostedt

kernel/trace/trace_events.c

@@ -1546,19 +1546,18 @@ event_enable_write(struct file *filp, const char __user *ubuf, size_t cnt,
 	if (ret)
 		return ret;
 
+	guard(mutex)(&event_mutex);
+
 	switch (val) {
 	case 0:
 	case 1:
-		mutex_lock(&event_mutex);
 		file = event_file_file(filp);
-		if (likely(file)) {
-			ret = tracing_update_buffers(file->tr);
-			if (ret >= 0)
-				ret = ftrace_event_enable_disable(file, val);
-		} else {
-			ret = -ENODEV;
-		}
-		mutex_unlock(&event_mutex);
+		if (!file)
+			return -ENODEV;
+		ret = tracing_update_buffers(file->tr);
+		if (ret < 0)
+			return ret;
+		ret = ftrace_event_enable_disable(file, val);
 		if (ret < 0)
 			return ret;
 		break;
@@ -2145,7 +2144,7 @@ event_pid_write(struct file *filp, const char __user *ubuf,
 	if (ret < 0)
 		return ret;
 
-	mutex_lock(&event_mutex);
+	guard(mutex)(&event_mutex);
 
 	if (type == TRACE_PIDS) {
 		filtered_pids = rcu_dereference_protected(tr->filtered_pids,
@@ -2161,7 +2160,7 @@ event_pid_write(struct file *filp, const char __user *ubuf,
 
 	ret = trace_pid_write(filtered_pids, &pid_list, ubuf, cnt);
 	if (ret < 0)
-		goto out;
+		return ret;
 
 	if (type == TRACE_PIDS)
 		rcu_assign_pointer(tr->filtered_pids, pid_list);
@@ -2186,11 +2185,7 @@ event_pid_write(struct file *filp, const char __user *ubuf,
 	 */
 	on_each_cpu(ignore_task_cpu, tr, 1);
 
- out:
-	mutex_unlock(&event_mutex);
-
-	if (ret > 0)
-		*ppos += ret;
+	*ppos += ret;
 
 	return ret;
 }
@@ -3257,13 +3252,13 @@ int trace_add_event_call(struct trace_event_call *call)
 	int ret;
 	lockdep_assert_held(&event_mutex);
 
-	mutex_lock(&trace_types_lock);
+	guard(mutex)(&trace_types_lock);
 
 	ret = __register_event(call, NULL);
-	if (ret >= 0)
-		__add_event_to_tracers(call);
+	if (ret < 0)
+		return ret;
 
-	mutex_unlock(&trace_types_lock);
+	__add_event_to_tracers(call);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(trace_add_event_call);
@@ -3517,30 +3512,21 @@ struct trace_event_file *trace_get_event_file(const char *instance,
 			return ERR_PTR(ret);
 	}
 
-	mutex_lock(&event_mutex);
+	guard(mutex)(&event_mutex);
 
 	file = find_event_file(tr, system, event);
 	if (!file) {
 		trace_array_put(tr);
-		ret = -EINVAL;
-		goto out;
+		return ERR_PTR(-EINVAL);
 	}
 
 	/* Don't let event modules unload while in use */
 	ret = trace_event_try_get_ref(file->event_call);
 	if (!ret) {
 		trace_array_put(tr);
-		ret = -EBUSY;
-		goto out;
+		return ERR_PTR(-EBUSY);
 	}
 
-	ret = 0;
- out:
-	mutex_unlock(&event_mutex);
-
-	if (ret)
-		file = ERR_PTR(ret);
-
 	return file;
 }
 EXPORT_SYMBOL_GPL(trace_get_event_file);
@@ -3778,12 +3764,11 @@ event_enable_func(struct trace_array *tr, struct ftrace_hash *hash,
 
 	event = strsep(&param, ":");
 
-	mutex_lock(&event_mutex);
+	guard(mutex)(&event_mutex);
 
-	ret = -EINVAL;
 	file = find_event_file(tr, system, event);
 	if (!file)
-		goto out;
+		return -EINVAL;
 
 	enable = strcmp(cmd, ENABLE_EVENT_STR) == 0;
 
@@ -3792,40 +3777,34 @@ event_enable_func(struct trace_array *tr, struct ftrace_hash *hash,
 	else
 		ops = param ? &event_disable_count_probe_ops : &event_disable_probe_ops;
 
-	if (glob[0] == '!') {
-		ret = unregister_ftrace_function_probe_func(glob+1, tr, ops);
-		goto out;
-	}
-
-	ret = -ENOMEM;
+	if (glob[0] == '!')
+		return unregister_ftrace_function_probe_func(glob+1, tr, ops);
 
 	if (param) {
 		number = strsep(&param, ":");
 
-		ret = -EINVAL;
 		if (!strlen(number))
-			goto out;
+			return -EINVAL;
 
 		/*
 		 * We use the callback data field (which is a pointer)
 		 * as our counter.
 		 */
 		ret = kstrtoul(number, 0, &count);
 		if (ret)
-			goto out;
+			return ret;
 	}
 
 	/* Don't let event modules unload while probe registered */
 	ret = trace_event_try_get_ref(file->event_call);
-	if (!ret) {
-		ret = -EBUSY;
-		goto out;
-	}
+	if (!ret)
+		return -EBUSY;
 
 	ret = __ftrace_event_enable_disable(file, 1, 1);
 	if (ret < 0)
 		goto out_put;
 
+	ret = -ENOMEM;
 	data = kzalloc(sizeof(*data), GFP_KERNEL);
 	if (!data)
 		goto out_put;
@@ -3840,23 +3819,20 @@ event_enable_func(struct trace_array *tr, struct ftrace_hash *hash,
 	 * but if it didn't find any functions it returns zero.
 	 * Consider no functions a failure too.
 	 */
-	if (!ret) {
-		ret = -ENOENT;
-		goto out_disable;
-	} else if (ret < 0)
-		goto out_disable;
+
 	/* Just return zero, not the number of enabled functions */
-	ret = 0;
- out:
-	mutex_unlock(&event_mutex);
-	return ret;
+	if (ret > 0)
+		return 0;
 
- out_disable:
 	kfree(data);
+
+	if (!ret)
+		ret = -ENOENT;
+
 	__ftrace_event_enable_disable(file, 0, 1);
  out_put:
 	trace_event_put_ref(file->event_call);
-	goto out;
+	return ret;
 }
 
 static struct ftrace_func_command event_enable_cmd = {
@@ -4079,20 +4055,17 @@ early_event_add_tracer(struct dentry *parent, struct trace_array *tr)
 {
 	int ret;
 
-	mutex_lock(&event_mutex);
+	guard(mutex)(&event_mutex);
 
 	ret = create_event_toplevel_files(parent, tr);
 	if (ret)
-		goto out_unlock;
+		return ret;
 
 	down_write(&trace_event_sem);
 	__trace_early_add_event_dirs(tr);
 	up_write(&trace_event_sem);
 
- out_unlock:
-	mutex_unlock(&event_mutex);
-
-	return ret;
+	return 0;
 }
 
 /* Must be called with event_mutex held */