[PATCH] g_file_storage: fix obscure race condition

This patch (as575) fixes an unlikely race in the g_file_storage driver.
The problem can occur only when the driver is unbound before its
initialization routine has finished.

I also took the opportunity to replace kmalloc/memset with kzalloc.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/file_storage.c

@@ -3823,12 +3823,11 @@ static int __init fsg_bind(struct usb_gadget *gadget)
 
 	/* Create the LUNs, open their backing files, and register the
 	 * LUN devices in sysfs. */
-	fsg->luns = kmalloc(i * sizeof(struct lun), GFP_KERNEL);
+	fsg->luns = kzalloc(i * sizeof(struct lun), GFP_KERNEL);
 	if (!fsg->luns) {
 		rc = -ENOMEM;
 		goto out;
 	}
-	memset(fsg->luns, 0, i * sizeof(struct lun));
 	fsg->nluns = i;
 
 	for (i = 0; i < fsg->nluns; ++i) {
@@ -3989,6 +3988,11 @@ static int __init fsg_bind(struct usb_gadget *gadget)
 			mod_data.removable, mod_data.can_stall,
 			mod_data.buflen);
 	DBG(fsg, "I/O thread pid: %d\n", fsg->thread_task->pid);
+
+	set_bit(REGISTERED, &fsg->atomic_bitflags);
+
+	/* Tell the thread to start working */
+	wake_up_process(fsg->thread_task);
 	return 0;
 
 autoconf_fail:
@@ -4051,10 +4055,9 @@ static int __init fsg_alloc(void)
 {
 	struct fsg_dev		*fsg;
 
-	fsg = kmalloc(sizeof *fsg, GFP_KERNEL);
+	fsg = kzalloc(sizeof *fsg, GFP_KERNEL);
 	if (!fsg)
 		return -ENOMEM;
-	memset(fsg, 0, sizeof *fsg);
 	spin_lock_init(&fsg->lock);
 	init_rwsem(&fsg->filesem);
 	init_waitqueue_head(&fsg->thread_wqh);
@@ -4080,15 +4083,9 @@ static int __init fsg_init(void)
 	if ((rc = fsg_alloc()) != 0)
 		return rc;
 	fsg = the_fsg;
-	if ((rc = usb_gadget_register_driver(&fsg_driver)) != 0) {
+	if ((rc = usb_gadget_register_driver(&fsg_driver)) != 0)
 		fsg_free(fsg);
-		return rc;
-	}
-	set_bit(REGISTERED, &fsg->atomic_bitflags);
-
-	/* Tell the thread to start working */
-	wake_up_process(fsg->thread_task);
-	return 0;
+	return rc;
 }
 module_init(fsg_init);