Revert "tracing: Have trace_event_file have ref counters"

This reverts commit a98172e36e which is
commit bb32500fb9b78215e4ef6ee8b4345c5f5d7eafb4 upstream.

It breaks the current Android ABI, and if needed, can be brought back in
an abi-safe way in the future.

Bug: 161946584
Change-Id: If981a67442122352b1836c6e75ba2a462cbc731d
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

include/linux/trace_events.h

@@ -365,7 +365,6 @@ enum {
 	EVENT_FILE_FL_TRIGGER_COND_BIT,
 	EVENT_FILE_FL_PID_FILTER_BIT,
 	EVENT_FILE_FL_WAS_ENABLED_BIT,
-	EVENT_FILE_FL_FREED_BIT,
 };
 
 extern struct trace_event_file *trace_get_event_file(const char *instance,
@@ -504,7 +503,6 @@ extern int __kprobe_event_add_fields(struct dynevent_cmd *cmd, ...);
  *  TRIGGER_COND  - When set, one or more triggers has an associated filter
  *  PID_FILTER    - When set, the event is filtered based on pid
  *  WAS_ENABLED   - Set when enabled to know to clear trace on module removal
- *  FREED         - File descriptor is freed, all fields should be considered invalid
  */
 enum {
 	EVENT_FILE_FL_ENABLED		= (1 << EVENT_FILE_FL_ENABLED_BIT),
@@ -518,7 +516,6 @@ enum {
 	EVENT_FILE_FL_TRIGGER_COND	= (1 << EVENT_FILE_FL_TRIGGER_COND_BIT),
 	EVENT_FILE_FL_PID_FILTER	= (1 << EVENT_FILE_FL_PID_FILTER_BIT),
 	EVENT_FILE_FL_WAS_ENABLED	= (1 << EVENT_FILE_FL_WAS_ENABLED_BIT),
-	EVENT_FILE_FL_FREED		= (1 << EVENT_FILE_FL_FREED_BIT),
 };
 
 struct trace_event_file {
@@ -547,7 +544,6 @@ struct trace_event_file {
 	 * caching and such. Which is mostly OK ;-)
 	 */
 	unsigned long		flags;
-	atomic_t		ref;	/* ref count for opened files */
 	atomic_t		sm_ref;	/* soft-mode reference counter */
 	atomic_t		tm_ref;	/* trigger-mode reference counter */
 };

kernel/trace/trace.c

@@ -4507,20 +4507,6 @@ int tracing_open_file_tr(struct inode *inode, struct file *filp)
 	if (ret)
 		return ret;
 
-	mutex_lock(&event_mutex);
-
-	/* Fail if the file is marked for removal */
-	if (file->flags & EVENT_FILE_FL_FREED) {
-		trace_array_put(file->tr);
-		ret = -ENODEV;
-	} else {
-		event_file_get(file);
-	}
-
-	mutex_unlock(&event_mutex);
-	if (ret)
-		return ret;
-
 	filp->private_data = inode->i_private;
 
 	return 0;
@@ -4531,7 +4517,6 @@ int tracing_release_file_tr(struct inode *inode, struct file *filp)
 	struct trace_event_file *file = inode->i_private;
 
 	trace_array_put(file->tr);
-	event_file_put(file);
 
 	return 0;
 }

kernel/trace/trace.h

@@ -1780,9 +1780,6 @@ extern int register_event_command(struct event_command *cmd);
 extern int unregister_event_command(struct event_command *cmd);
 extern int register_trigger_hist_enable_disable_cmds(void);
 
-extern void event_file_get(struct trace_event_file *file);
-extern void event_file_put(struct trace_event_file *file);
-
 /**
  * struct event_trigger_ops - callbacks for trace event triggers
  *

kernel/trace/trace_events.c

@@ -746,38 +746,26 @@ static void remove_subsystem(struct trace_subsystem_dir *dir)
 	}
 }
 
-void event_file_get(struct trace_event_file *file)
-{
-	atomic_inc(&file->ref);
-}
-
-void event_file_put(struct trace_event_file *file)
-{
-	if (WARN_ON_ONCE(!atomic_read(&file->ref))) {
-		if (file->flags & EVENT_FILE_FL_FREED)
-			kmem_cache_free(file_cachep, file);
-		return;
-	}
-
-	if (atomic_dec_and_test(&file->ref)) {
-		/* Count should only go to zero when it is freed */
-		if (WARN_ON_ONCE(!(file->flags & EVENT_FILE_FL_FREED)))
-			return;
-		kmem_cache_free(file_cachep, file);
-	}
-}
-
 static void remove_event_file_dir(struct trace_event_file *file)
 {
 	struct dentry *dir = file->dir;
+	struct dentry *child;
 
-	tracefs_remove(dir);
+	if (dir) {
+		spin_lock(&dir->d_lock);	/* probably unneeded */
+		list_for_each_entry(child, &dir->d_subdirs, d_child) {
+			if (d_really_is_positive(child))	/* probably unneeded */
+				d_inode(child)->i_private = NULL;
+		}
+		spin_unlock(&dir->d_lock);
+
+		tracefs_remove(dir);
+	}
 
 	list_del(&file->list);
 	remove_subsystem(file->system);
 	free_event_filter(file->filter);
-	file->flags |= EVENT_FILE_FL_FREED;
+	kmem_cache_free(file_cachep, file);
-	event_file_put(file);
 }
 
 /*
@@ -1150,7 +1138,7 @@ event_enable_read(struct file *filp, char __user *ubuf, size_t cnt,
 		flags = file->flags;
 	mutex_unlock(&event_mutex);
 
-	if (!file || flags & EVENT_FILE_FL_FREED)
+	if (!file)
 		return -ENODEV;
 
 	if (flags & EVENT_FILE_FL_ENABLED &&
@@ -1188,7 +1176,7 @@ event_enable_write(struct file *filp, const char __user *ubuf, size_t cnt,
 		ret = -ENODEV;
 		mutex_lock(&event_mutex);
 		file = event_file_data(filp);
-		if (likely(file && !(file->flags & EVENT_FILE_FL_FREED)))
+		if (likely(file))
 			ret = ftrace_event_enable_disable(file, val);
 		mutex_unlock(&event_mutex);
 		break;
@@ -1457,7 +1445,7 @@ event_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
 
 	mutex_lock(&event_mutex);
 	file = event_file_data(filp);
-	if (file && !(file->flags & EVENT_FILE_FL_FREED))
+	if (file)
 		print_event_filter(file, s);
 	mutex_unlock(&event_mutex);
 
@@ -2494,7 +2482,6 @@ trace_create_new_event(struct trace_event_call *call,
 	atomic_set(&file->tm_ref, 0);
 	INIT_LIST_HEAD(&file->triggers);
 	list_add(&file->list, &tr->events);
-	event_file_get(file);
 
 	return file;
 }

kernel/trace/trace_events_filter.c

@@ -1893,9 +1893,6 @@ int apply_event_filter(struct trace_event_file *file, char *filter_string)
 	struct event_filter *filter = NULL;
 	int err;
 
-	if (file->flags & EVENT_FILE_FL_FREED)
-		return -ENODEV;
-
 	if (!strcmp(strstrip(filter_string), "0")) {
 		filter_disable(file);
 		filter = event_filter(file);