firewire: cdev: reference-count client instances

The lifetime of struct client instances must be longer than the lifetime
of any client resource.

This fixes a possible race between fw_device_op_release and transaction
completions.  It also prepares for new ioctls for isochronous resource
management which will involve delayed processing of client resources.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Reviewed-by: David Moore <dcm@acm.org>

1 files changed, 46 insertions, 9 deletions

diff --git a/drivers/firewire/fw-cdev.c b/drivers/firewire/fw-cdev.c
index ead5c7b06ec1..81362c14ef44 100644
--- a/drivers/firewire/fw-cdev.c
+++ b/drivers/firewire/fw-cdev.c
@@ -20,6 +20,7 @@
 
 #include <linux/module.h>
 #include <linux/kernel.h>
+#include <linux/kref.h>
 #include <linux/wait.h>
 #include <linux/errno.h>
 #include <linux/device.h>
@@ -94,8 +95,27 @@ struct client {
         unsigned long vm_start;
 
         struct list_head link;
+        struct kref kref;
 };
 
+static inline void client_get(struct client *client)
+{
+        kref_get(&client->kref);
+}
+
+static void client_release(struct kref *kref)
+{
+        struct client *client = container_of(kref, struct client, kref);
+
+        fw_device_put(client->device);
+        kfree(client);
+}
+
+static void client_put(struct client *client)
+{
+        kref_put(&client->kref, client_release);
+}
+
 static inline void __user *u64_to_uptr(__u64 value)
 {
         return (void __user *)(unsigned long)value;
@@ -131,6 +151,7 @@ static int fw_device_op_open(struct inode *inode, struct file *file)
         idr_init(&client->resource_idr);
         INIT_LIST_HEAD(&client->event_list);
         init_waitqueue_head(&client->wait);
+        kref_init(&client->kref);
 
         file->private_data = client;
 
@@ -326,6 +347,8 @@ static int add_client_resource(struct client *client,
         else
                 ret = idr_get_new(&client->resource_idr, resource,
                                   &resource->handle);
+        if (ret >= 0)
+                client_get(client);
         spin_unlock_irqrestore(&client->lock, flags);
 
         if (ret == -EAGAIN)
@@ -358,6 +381,8 @@ static int release_client_resource(struct client *client, u32 handle,
         else
                 r->release(client, r);
 
+        client_put(client);
+
         return 0;
 }
 
@@ -385,11 +410,21 @@ static void complete_transaction(struct fw_card *card, int rcode,
 
         spin_lock_irqsave(&client->lock, flags);
         /*
-         * If called while in shutdown, the idr tree must be left untouched.
-         * The idr handle will be removed later.
+         * 1. If called while in shutdown, the idr tree must be left untouched.
+         *    The idr handle will be removed and the client reference will be
+         *    dropped later.
+         * 2. If the call chain was release_client_resource ->
+         *    release_transaction -> complete_transaction (instead of a normal
+         *    conclusion of the transaction), i.e. if this resource was already
+         *    unregistered from the idr, the client reference will be dropped
+         *    by release_client_resource and we must not drop it here.
          */
-        if (!client->in_shutdown)
+        if (!client->in_shutdown &&
+            idr_find(&client->resource_idr, response->resource.handle)) {
                 idr_remove(&client->resource_idr, response->resource.handle);
+                /* Drop the idr's reference */
+                client_put(client);
+        }
         spin_unlock_irqrestore(&client->lock, flags);
 
         r->type   = FW_CDEV_EVENT_RESPONSE;
@@ -408,6 +443,9 @@ static void complete_transaction(struct fw_card *card, int rcode,
         else
                 queue_event(client, &response->event, r, sizeof(*r) + r->length,
                             NULL, 0);
+
+        /* Drop the transaction callback's reference */
+        client_put(client);
 }
 
 static int ioctl_send_request(struct client *client, void *buffer)
@@ -459,6 +497,9 @@ static int ioctl_send_request(struct client *client, void *buffer)
         if (ret < 0)
                 goto failed;
 
+        /* Get a reference for the transaction callback */
+        client_get(client);
+
         fw_send_request(device->card, &response->transaction,
                         request->tcode & 0x1f,
                         device->node->node_id,
@@ -1044,6 +1085,7 @@ static int shutdown_resource(int id, void *p, void *data)
         struct client *client = data;
 
         r->release(client, r);
+        client_put(client);
 
         return 0;
 }
@@ -1076,12 +1118,7 @@ static int fw_device_op_release(struct inode *inode, struct file *file)
         list_for_each_entry_safe(e, next_e, &client->event_list, link)
                 kfree(e);
 
-        /*
-         * FIXME: client should be reference-counted.  It's extremely unlikely
-         * but there may still be transactions being completed at this point.
-         */
-        fw_device_put(client->device);
-        kfree(client);
+        client_put(client);
 
         return 0;
 }