ion:synchronize debugfs callback and ion_client_destroy

There are race condition B/T ion_client_destroy and debugfs callbacks.
Let's use a mutex to synchronize them.
Signed-off-by: Neil Zhang <neilzhang1123@hotmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ion/ion.c

@@ -677,6 +677,34 @@ void ion_unmap_kernel(struct ion_client *client, struct ion_handle *handle)
 }
 EXPORT_SYMBOL(ion_unmap_kernel);
 
+static struct mutex debugfs_mutex;
+static struct rb_root *ion_root_client;
+static int is_client_alive(struct ion_client *client)
+{
+	struct rb_node *node;
+	struct ion_client *tmp;
+	struct ion_device *dev;
+
+	node = ion_root_client->rb_node;
+	dev = container_of(ion_root_client, struct ion_device, clients);
+
+	down_read(&dev->lock);
+	while (node) {
+		tmp = rb_entry(node, struct ion_client, node);
+		if (client < tmp) {
+			node = node->rb_left;
+		} else if (client > tmp) {
+			node = node->rb_right;
+		} else {
+			up_read(&dev->lock);
+			return 1;
+		}
+	}
+
+	up_read(&dev->lock);
+	return 0;
+}
+
 static int ion_debug_client_show(struct seq_file *s, void *unused)
 {
 	struct ion_client *client = s->private;
@@ -685,6 +713,14 @@ static int ion_debug_client_show(struct seq_file *s, void *unused)
 	const char *names[ION_NUM_HEAP_IDS] = {NULL};
 	int i;
 
+	mutex_lock(&debugfs_mutex);
+	if (!is_client_alive(client)) {
+		seq_printf(s, "ion_client 0x%p dead, can't dump its buffers\n",
+			   client);
+		mutex_unlock(&debugfs_mutex);
+		return 0;
+	}
+
 	mutex_lock(&client->lock);
 	for (n = rb_first(&client->handles); n; n = rb_next(n)) {
 		struct ion_handle *handle = rb_entry(n, struct ion_handle,
@@ -696,6 +732,7 @@ static int ion_debug_client_show(struct seq_file *s, void *unused)
 		sizes[id] += handle->buffer->size;
 	}
 	mutex_unlock(&client->lock);
+	mutex_unlock(&debugfs_mutex);
 
 	seq_printf(s, "%16.16s: %16.16s\n", "heap_name", "size_in_bytes");
 	for (i = 0; i < ION_NUM_HEAP_IDS; i++) {
@@ -832,6 +869,7 @@ void ion_client_destroy(struct ion_client *client)
 	struct rb_node *n;
 
 	pr_debug("%s: %d\n", __func__, __LINE__);
+	mutex_lock(&debugfs_mutex);
 	while ((n = rb_first(&client->handles))) {
 		struct ion_handle *handle = rb_entry(n, struct ion_handle,
 						     node);
@@ -850,6 +888,7 @@ void ion_client_destroy(struct ion_client *client)
 	kfree(client->display_name);
 	kfree(client->name);
 	kfree(client);
+	mutex_unlock(&debugfs_mutex);
 }
 EXPORT_SYMBOL(ion_client_destroy);
 
@@ -1415,6 +1454,7 @@ static int ion_debug_heap_show(struct seq_file *s, void *unused)
 	seq_printf(s, "%16s %16s %16s\n", "client", "pid", "size");
 	seq_puts(s, "----------------------------------------------------\n");
 
+	mutex_lock(&debugfs_mutex);
 	for (n = rb_first(&dev->clients); n; n = rb_next(n)) {
 		struct ion_client *client = rb_entry(n, struct ion_client,
 						     node);
@@ -1433,6 +1473,8 @@ static int ion_debug_heap_show(struct seq_file *s, void *unused)
 				   client->pid, size);
 		}
 	}
+	mutex_unlock(&debugfs_mutex);
+
 	seq_puts(s, "----------------------------------------------------\n");
 	seq_puts(s, "orphaned allocations (info is from last known client):\n");
 	mutex_lock(&dev->buffer_lock);
@@ -1617,6 +1659,8 @@ struct ion_device *ion_device_create(long (*custom_ioctl)
 	init_rwsem(&idev->lock);
 	plist_head_init(&idev->heaps);
 	idev->clients = RB_ROOT;
+	ion_root_client = &idev->clients;
+	mutex_init(&debugfs_mutex);
 	return idev;
 }
 EXPORT_SYMBOL(ion_device_create);