BACKPORT: ion:synchronize debugfs callback and ion_client_destroy

(cherry picked from commit 948c4db4ee10d85fe78ed3755dcaeb85cd37a148)

There are race condition B/T ion_client_destroy and debugfs callbacks.
Let's use a mutex to synchronize them.

Change-Id: I4d73b258ac1fb67604b62f237da0e004275fd3da
Signed-off-by: Neil Zhang <neilzhang1123@hotmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 43 insertions, 0 deletions

diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
index d8dfe66e2..d6fa9f639 100755
--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -881,6 +881,34 @@ 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_client_validate(struct ion_device *dev,
 				struct ion_client *client)
 {
@@ -915,6 +943,14 @@ static int ion_debug_client_show(struct seq_file *s, void *unused)
 
         seq_printf(s, "%16.s %8.s %8.s %8.s %8.s %8.s\n", "heap_name","pid", "size", "handle_count","handle","buffer");
 
+	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,
@@ -930,6 +966,7 @@ static int ion_debug_client_show(struct seq_file *s, void *unused)
 			       client->pid, buffer->size, buffer->handle_count, handle, buffer);
 	}
 	mutex_unlock(&client->lock);
+	mutex_unlock(&debugfs_mutex);
 
         seq_printf(s, "----------------------------------------------------\n");
 
@@ -1086,6 +1123,7 @@ void __ion_client_destroy(struct ion_client *client, int from_kern)
 	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);
@@ -1114,6 +1152,7 @@ void __ion_client_destroy(struct ion_client *client, int from_kern)
 #endif
 
 	kfree(client);
+	mutex_unlock(&debugfs_mutex);
 }
 
 void ion_client_destroy(struct ion_client *client)
@@ -1750,6 +1789,7 @@ static int ion_debug_heap_show(struct seq_file *s, void *unused)
 	seq_puts(s, "----------------------------------------------------\n");
 
 	down_read(&dev->lock);
+	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);
@@ -1768,6 +1808,7 @@ static int ion_debug_heap_show(struct seq_file *s, void *unused)
 		}
 	}
 	up_read(&dev->lock);
+	mutex_unlock(&debugfs_mutex);
 
 	seq_puts(s, "----------------------------------------------------\n");
 	seq_puts(s, "orphaned allocations (info is from last known client):\n");
@@ -2001,6 +2042,8 @@ debugfs_done:
 	/* Create ION Debug DB Root */
 	ion_debug_create_db(idev->debug_root);
 #endif
+	ion_root_client = &idev->clients;
+	mutex_init(&debugfs_mutex);
 	return idev;
 }