USB: Increase usbfs transfer limit

Promote a variable keeping track of USB transfer memory usage to a
wider data type and allow for higher bandwidth transfers from a large
number of USB devices connected to a single host.
Signed-off-by: Mateusz Berezecki <mateuszb@fastmail.fm>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/devio.c

@@ -134,42 +134,35 @@ enum snoop_when {
 #define USB_DEVICE_DEV		MKDEV(USB_DEVICE_MAJOR, 0)
 
 /* Limit on the total amount of memory we can allocate for transfers */
-static unsigned usbfs_memory_mb = 16;
+static u32 usbfs_memory_mb = 16;
 module_param(usbfs_memory_mb, uint, 0644);
 MODULE_PARM_DESC(usbfs_memory_mb,
 		"maximum MB allowed for usbfs buffers (0 = no limit)");
 
-/* Hard limit, necessary to avoid arithmetic overflow */
-#define USBFS_XFER_MAX		(UINT_MAX / 2 - 1000000)
-
-static atomic_t usbfs_memory_usage;	/* Total memory currently allocated */
+static atomic64_t usbfs_memory_usage;	/* Total memory currently allocated */
 
 /* Check whether it's okay to allocate more memory for a transfer */
-static int usbfs_increase_memory_usage(unsigned amount)
+static int usbfs_increase_memory_usage(u64 amount)
 {
-	unsigned lim;
+	u64 lim;
 
-	/*
-	 * Convert usbfs_memory_mb to bytes, avoiding overflows.
-	 * 0 means use the hard limit (effectively unlimited).
-	 */
 	lim = ACCESS_ONCE(usbfs_memory_mb);
-	if (lim == 0 || lim > (USBFS_XFER_MAX >> 20))
-		lim = USBFS_XFER_MAX;
-	else
-		lim <<= 20;
+	lim <<= 20;
 
-	atomic_add(amount, &usbfs_memory_usage);
-	if (atomic_read(&usbfs_memory_usage) <= lim)
-		return 0;
-	atomic_sub(amount, &usbfs_memory_usage);
-	return -ENOMEM;
+	atomic64_add(amount, &usbfs_memory_usage);
+
+	if (lim > 0 && atomic64_read(&usbfs_memory_usage) > lim) {
+		atomic64_sub(amount, &usbfs_memory_usage);
+		return -ENOMEM;
+	}
+
+	return 0;
 }
 
 /* Memory for a transfer is being deallocated */
-static void usbfs_decrease_memory_usage(unsigned amount)
+static void usbfs_decrease_memory_usage(u64 amount)
 {
-	atomic_sub(amount, &usbfs_memory_usage);
+	atomic64_sub(amount, &usbfs_memory_usage);
 }
 
 static int connected(struct usb_dev_state *ps)
@@ -1191,7 +1184,7 @@ static int proc_bulk(struct usb_dev_state *ps, void __user *arg)
 	if (!usb_maxpacket(dev, pipe, !(bulk.ep & USB_DIR_IN)))
 		return -EINVAL;
 	len1 = bulk.len;
-	if (len1 >= USBFS_XFER_MAX)
+	if (len1 >= (INT_MAX - sizeof(struct urb)))
 		return -EINVAL;
 	ret = usbfs_increase_memory_usage(len1 + sizeof(struct urb));
 	if (ret)
@@ -1584,10 +1577,6 @@ static int proc_do_submiturb(struct usb_dev_state *ps, struct usbdevfs_urb *uurb
 		return -EINVAL;
 	}
 
-	if (uurb->buffer_length >= USBFS_XFER_MAX) {
-		ret = -EINVAL;
-		goto error;
-	}
 	if (uurb->buffer_length > 0 &&
 			!access_ok(is_in ? VERIFY_WRITE : VERIFY_READ,
 				uurb->buffer, uurb->buffer_length)) {