usb-skeleton: don't submit URBs after disconnection

This patch (as712b) is a slight revision of one submitted earlier.  It
fixes the usb-skeleton example driver so that it won't try to submit
URBs after skel_disconnect() has returned.  This could cause errors, if
the driver was unbound and then a different driver was bound to the
device.  It also fixes a couple of small bugs in the skel_write()
routine.

The revised patch uses a slightly different test, suggested by Dave
Brownell, for determining whether to free a transfer buffer.  It's a
little clearer than the earlier version.


Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 33 insertions, 7 deletions

diff --git a/drivers/usb/usb-skeleton.c b/drivers/usb/usb-skeleton.c
index b362039792b3..33f0e81c58d3 100644
--- a/drivers/usb/usb-skeleton.c
+++ b/drivers/usb/usb-skeleton.c
@@ -1,5 +1,5 @@
 /*
- * USB Skeleton driver - 2.0
+ * USB Skeleton driver - 2.1
  *
  * Copyright (C) 2001-2004 Greg Kroah-Hartman (greg@kroah.com)
  *
@@ -8,8 +8,7 @@
  *      published by the Free Software Foundation, version 2.
  *
  * This driver is based on the 2.6.3 version of drivers/usb/usb-skeleton.c 
- * but has been rewritten to be easy to read and use, as no locks are now
- * needed anymore.
+ * but has been rewritten to be easier to read and use.
  *
  */
 
@@ -21,6 +20,7 @@
 #include <linux/kref.h>
 #include <asm/uaccess.h>
 #include <linux/usb.h>
+#include <linux/mutex.h>
 
 
 /* Define these values to match your devices */
@@ -52,6 +52,7 @@ struct usb_skel {
         __u8                    bulk_in_endpointAddr;   /* the address of the bulk in endpoint */
         __u8                    bulk_out_endpointAddr;  /* the address of the bulk out endpoint */
         struct kref             kref;
+        struct mutex            io_mutex;               /* synchronize I/O with disconnect */
 };
 #define to_skel_dev(d) container_of(d, struct usb_skel, kref)
 
@@ -119,7 +120,13 @@ static ssize_t skel_read(struct file *file, char *buffer, size_t count, loff_t *
         int bytes_read;
 
         dev = (struct usb_skel *)file->private_data;
-        
+
+        mutex_lock(&dev->io_mutex);
+        if (!dev->interface) {          /* disconnect() was called */
+                retval = -ENODEV;
+                goto exit;
+        }
+
         /* do a blocking bulk read to get data from the device */
         retval = usb_bulk_msg(dev->udev,
                               usb_rcvbulkpipe(dev->udev, dev->bulk_in_endpointAddr),
@@ -135,6 +142,8 @@ static ssize_t skel_read(struct file *file, char *buffer, size_t count, loff_t *
                         retval = bytes_read;
         }
 
+exit:
+        mutex_unlock(&dev->io_mutex);
         return retval;
 }
 
@@ -179,6 +188,12 @@ static ssize_t skel_write(struct file *file, const char *user_buffer, size_t cou
                 goto exit;
         }
 
+        mutex_lock(&dev->io_mutex);
+        if (!dev->interface) {          /* disconnect() was called */
+                retval = -ENODEV;
+                goto error;
+        }
+
         /* create a urb, and a buffer for it, and copy the data to the urb */
         urb = usb_alloc_urb(0, GFP_KERNEL);
         if (!urb) {
@@ -213,13 +228,18 @@ static ssize_t skel_write(struct file *file, const char *user_buffer, size_t cou
         /* release our reference to this urb, the USB core will eventually free it entirely */
         usb_free_urb(urb);
 
-exit:
+        mutex_unlock(&dev->io_mutex);
         return writesize;
 
 error:
-        usb_buffer_free(dev->udev, writesize, buf, urb->transfer_dma);
-        usb_free_urb(urb);
+        if (urb) {
+                usb_buffer_free(dev->udev, writesize, buf, urb->transfer_dma);
+                usb_free_urb(urb);
+        }
+        mutex_unlock(&dev->io_mutex);
         up(&dev->limit_sem);
+
+exit:
         return retval;
 }
 
@@ -258,6 +278,7 @@ static int skel_probe(struct usb_interface *interface, const struct usb_device_i
         }
         kref_init(&dev->kref);
         sema_init(&dev->limit_sem, WRITES_IN_FLIGHT);
+        mutex_init(&dev->io_mutex);
 
         dev->udev = usb_get_dev(interface_to_usbdev(interface));
         dev->interface = interface;
@@ -334,6 +355,11 @@ static void skel_disconnect(struct usb_interface *interface)
         /* give back our minor */
         usb_deregister_dev(interface, &skel_class);
 
+        /* prevent more I/O from starting */
+        mutex_lock(&dev->io_mutex);
+        dev->interface = NULL;
+        mutex_unlock(&dev->io_mutex);
+
         unlock_kernel();
 
         /* decrement our usage count */