3 files changed, 55 insertions, 20 deletions

diff --git a/Documentation/usb/persist.txt b/Documentation/usb/persist.txt
index bea58dbd30fe..d56cb1a11550 100644
--- a/Documentation/usb/persist.txt
+++ b/Documentation/usb/persist.txt
@@ -136,10 +136,10 @@ aren't guaranteed to be 100% accurate.
 
 If you replace one USB device with another of the same type (same
 manufacturer, same IDs, and so on) there's an excellent chance the
-kernel won't detect the change.  Serial numbers and other strings are
-not compared.  In many cases it wouldn't help if they were, because
-manufacturers frequently omit serial numbers entirely in their
-devices.
+kernel won't detect the change.  The serial number string and other
+descriptors are compared with the kernel's stored values, but this
+might not help since manufacturers frequently omit serial numbers
+entirely in their devices.
 
 Furthermore it's quite possible to leave a USB device exactly the same
 while changing its media.  If you replace the flash memory card in a
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 6dc589955d75..9fc5179dfc60 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -3010,16 +3010,36 @@ void usb_hub_cleanup(void)
         usb_deregister(&hub_driver);
 } /* usb_hub_cleanup() */
 
-static int config_descriptors_changed(struct usb_device *udev)
-{
-        unsigned                        index;
-        unsigned                        len = 0;
-        struct usb_config_descriptor    *buf;
+static int descriptors_changed(struct usb_device *udev,
+                struct usb_device_descriptor *old_device_descriptor)
+{
+        int             changed = 0;
+        unsigned        index;
+        unsigned        serial_len = 0;
+        unsigned        len;
+        unsigned        old_length;
+        int             length;
+        char            *buf;
+
+        if (memcmp(&udev->descriptor, old_device_descriptor,
+                        sizeof(*old_device_descriptor)) != 0)
+                return 1;
+
+        /* Since the idVendor, idProduct, and bcdDevice values in the
+         * device descriptor haven't changed, we will assume the
+         * Manufacturer and Product strings haven't changed either.
+         * But the SerialNumber string could be different (e.g., a
+         * different flash card of the same brand).
+         */
+        if (udev->serial)
+                serial_len = strlen(udev->serial) + 1;
 
+        len = serial_len;
         for (index = 0; index < udev->descriptor.bNumConfigurations; index++) {
-                if (len < le16_to_cpu(udev->config[index].desc.wTotalLength))
-                        len = le16_to_cpu(udev->config[index].desc.wTotalLength);
+                old_length = le16_to_cpu(udev->config[index].desc.wTotalLength);
+                len = max(len, old_length);
         }
+
         buf = kmalloc(len, GFP_NOIO);
         if (buf == NULL) {
                 dev_err(&udev->dev, "no mem to re-read configs after reset\n");
@@ -3027,25 +3047,41 @@ static int config_descriptors_changed(struct usb_device *udev)
                 return 1;
         }
         for (index = 0; index < udev->descriptor.bNumConfigurations; index++) {
-                int length;
-                int old_length = le16_to_cpu(udev->config[index].desc.wTotalLength);
-
+                old_length = le16_to_cpu(udev->config[index].desc.wTotalLength);
                 length = usb_get_descriptor(udev, USB_DT_CONFIG, index, buf,
                                 old_length);
-                if (length < old_length) {
+                if (length != old_length) {
                         dev_dbg(&udev->dev, "config index %d, error %d\n",
                                         index, length);
+                        changed = 1;
                         break;
                 }
                 if (memcmp (buf, udev->rawdescriptors[index], old_length)
                                 != 0) {
                         dev_dbg(&udev->dev, "config index %d changed (#%d)\n",
-                                index, buf->bConfigurationValue);
+                                index,
+                                ((struct usb_config_descriptor *) buf)->
+                                        bConfigurationValue);
+                        changed = 1;
                         break;
                 }
         }
+
+        if (!changed && serial_len) {
+                length = usb_string(udev, udev->descriptor.iSerialNumber,
+                                buf, serial_len);
+                if (length + 1 != serial_len) {
+                        dev_dbg(&udev->dev, "serial string error %d\n",
+                                        length);
+                        changed = 1;
+                } else if (memcmp(buf, udev->serial, length) != 0) {
+                        dev_dbg(&udev->dev, "serial string changed\n");
+                        changed = 1;
+                }
+        }
+
         kfree(buf);
-        return index != udev->descriptor.bNumConfigurations;
+        return changed;
 }
 
 /**
@@ -3118,8 +3154,7 @@ int usb_reset_device(struct usb_device *udev)
                 goto re_enumerate;
  
         /* Device might have changed firmware (DFU or similar) */
-        if (memcmp(&udev->descriptor, &descriptor, sizeof descriptor)
-                        || config_descriptors_changed (udev)) {
+        if (descriptors_changed(udev, &descriptor)) {
                 dev_info(&udev->dev, "device firmware changed\n");
                 udev->descriptor = descriptor;  /* for disconnect() calls */
                 goto re_enumerate;
diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
index c311f67b7f08..a3695b5115ff 100644
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -784,7 +784,7 @@ int usb_string(struct usb_device *dev, int index, char *buf, size_t size)
         if (size <= 0 || !buf || !index)
                 return -EINVAL;
         buf[0] = 0;
-        tbuf = kmalloc(256, GFP_KERNEL);
+        tbuf = kmalloc(256, GFP_NOIO);
         if (!tbuf)
                 return -ENOMEM;