[PATCH] USB: file-storage gadget: Add reference count for children

This patch (as601) adds a proper reference count to the file-storage
gadget's main data structure, to keep track of references held by child
devices (LUNs in this case).  Before this, the driver would wait for
each child to be released before unbinding.

While there's nothing really wrong with that (you can't create a hang by
doing "rmmod g_file_storage </sys/.../lun0/ro" since the open file will
prevent rmmod from running), the code might as well follow the standard
procedures.  Besides, this shrinks the size of the structure by a few
words...  :-)
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/file_storage.c

@@ -224,6 +224,7 @@
 #include <linux/fs.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
+#include <linux/kref.h>
 #include <linux/kthread.h>
 #include <linux/limits.h>
 #include <linux/list.h>
@@ -631,6 +632,9 @@ struct fsg_dev {
 	/* filesem protects: backing files in use */
 	struct rw_semaphore	filesem;
 
+	/* reference counting: wait until all LUNs are released */
+	struct kref		ref;
+
 	struct usb_ep		*ep0;		// Handy copy of gadget->ep0
 	struct usb_request	*ep0req;	// For control responses
 	volatile unsigned int	ep0_req_tag;
@@ -694,7 +698,6 @@ struct fsg_dev {
 	unsigned int		nluns;
 	struct lun		*luns;
 	struct lun		*curlun;
-	struct completion	lun_released;
 };
 
 typedef void (*fsg_routine_t)(struct fsg_dev *);
@@ -3642,11 +3645,19 @@ static DEVICE_ATTR(file, 0444, show_file, NULL);
 
 /*-------------------------------------------------------------------------*/
 
+static void fsg_release(struct kref *ref)
+{
+	struct fsg_dev	*fsg = container_of(ref, struct fsg_dev, ref);
+
+	kfree(fsg->luns);
+	kfree(fsg);
+}
+
 static void lun_release(struct device *dev)
 {
 	struct fsg_dev	*fsg = (struct fsg_dev *) dev_get_drvdata(dev);
 
-	complete(&fsg->lun_released);
+	kref_put(&fsg->ref, fsg_release);
 }
 
 static void fsg_unbind(struct usb_gadget *gadget)
@@ -3660,14 +3671,12 @@ static void fsg_unbind(struct usb_gadget *gadget)
 	clear_bit(REGISTERED, &fsg->atomic_bitflags);
 
 	/* Unregister the sysfs attribute files and the LUNs */
-	init_completion(&fsg->lun_released);
 	for (i = 0; i < fsg->nluns; ++i) {
 		curlun = &fsg->luns[i];
 		if (curlun->registered) {
 			device_remove_file(&curlun->dev, &dev_attr_ro);
 			device_remove_file(&curlun->dev, &dev_attr_file);
 			device_unregister(&curlun->dev);
-			wait_for_completion(&fsg->lun_released);
 			curlun->registered = 0;
 		}
 	}
@@ -3846,6 +3855,7 @@ static int __init fsg_bind(struct usb_gadget *gadget)
 			curlun->dev.release = lun_release;
 			device_create_file(&curlun->dev, &dev_attr_ro);
 			device_create_file(&curlun->dev, &dev_attr_file);
+			kref_get(&fsg->ref);
 		}
 
 		if (file[i] && *file[i]) {
@@ -4061,6 +4071,7 @@ static int __init fsg_alloc(void)
 		return -ENOMEM;
 	spin_lock_init(&fsg->lock);
 	init_rwsem(&fsg->filesem);
+	kref_init(&fsg->ref);
 	init_waitqueue_head(&fsg->thread_wqh);
 	init_completion(&fsg->thread_notifier);
 
@@ -4069,13 +4080,6 @@ static int __init fsg_alloc(void)
 }
 
 
-static void fsg_free(struct fsg_dev *fsg)
-{
-	kfree(fsg->luns);
-	kfree(fsg);
-}
-
-
 static int __init fsg_init(void)
 {
 	int		rc;
@@ -4085,7 +4089,7 @@ static int __init fsg_init(void)
 		return rc;
 	fsg = the_fsg;
 	if ((rc = usb_gadget_register_driver(&fsg_driver)) != 0)
-		fsg_free(fsg);
+		kref_put(&fsg->ref, fsg_release);
 	return rc;
 }
 module_init(fsg_init);
@@ -4103,6 +4107,6 @@ static void __exit fsg_cleanup(void)
 	wait_for_completion(&fsg->thread_notifier);
 
 	close_all_backing_files(fsg);
-	fsg_free(fsg);
+	kref_put(&fsg->ref, fsg_release);
 }
 module_exit(fsg_cleanup);