spidev: BKL removal

Another step to removing ->ioctl and to removing the BKL

[dbrownell@users.sourceforge.net: take final step; BKL not needed]
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/spi/spidev.c

@@ -228,7 +228,6 @@ static int spidev_message(struct spidev_data *spidev,
 	 * We walk the array of user-provided transfers, using each one
 	 * to initialize a kernel version of the same transfer.
 	 */
-	mutex_lock(&spidev->buf_lock);
 	buf = spidev->buffer;
 	total = 0;
 	for (n = n_xfers, k_tmp = k_xfers, u_tmp = u_xfers;
@@ -296,14 +295,12 @@ static int spidev_message(struct spidev_data *spidev,
 	status = total;
 
 done:
-	mutex_unlock(&spidev->buf_lock);
 	kfree(k_xfers);
 	return status;
 }
 
-static int
-spidev_ioctl(struct inode *inode, struct file *filp,
-		unsigned int cmd, unsigned long arg)
+static long
+spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	int			err = 0;
 	int			retval = 0;
@@ -341,6 +338,14 @@ spidev_ioctl(struct inode *inode, struct file *filp,
 	if (spi == NULL)
 		return -ESHUTDOWN;
 
+	/* use the buffer lock here for triple duty:
+	 *  - prevent I/O (from us) so calling spi_setup() is safe;
+	 *  - prevent concurrent SPI_IOC_WR_* from morphing
+	 *    data fields while SPI_IOC_RD_* reads them;
+	 *  - SPI_IOC_MESSAGE needs the buffer locked "normally".
+	 */
+	mutex_lock(&spidev->buf_lock);
+
 	switch (cmd) {
 	/* read requests */
 	case SPI_IOC_RD_MODE:
@@ -456,6 +461,8 @@ spidev_ioctl(struct inode *inode, struct file *filp,
 		kfree(ioc);
 		break;
 	}
+
+	mutex_unlock(&spidev->buf_lock);
 	spi_dev_put(spi);
 	return retval;
 }
@@ -533,7 +540,7 @@ static struct file_operations spidev_fops = {
 	 */
 	.write =	spidev_write,
 	.read =		spidev_read,
-	.ioctl =	spidev_ioctl,
+	.unlocked_ioctl = spidev_ioctl,
 	.open =		spidev_open,
 	.release =	spidev_release,
 };