spidev: BKL pushdown

Add the BKL to spidev_open(), even though the existing locking looks
adequate.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

drivers/spi/spidev.c

@@ -29,6 +29,7 @@
 #include <linux/errno.h>
 #include <linux/mutex.h>
 #include <linux/slab.h>
+#include <linux/smp_lock.h>
 
 #include <linux/spi/spi.h>
 #include <linux/spi/spidev.h>
@@ -393,6 +394,7 @@ static int spidev_open(struct inode *inode, struct file *filp)
 	struct spidev_data	*spidev;
 	int			status = -ENXIO;
 
+	lock_kernel();
 	mutex_lock(&device_list_lock);
 
 	list_for_each_entry(spidev, &device_list, device_entry) {
@@ -418,6 +420,7 @@ static int spidev_open(struct inode *inode, struct file *filp)
 		pr_debug("spidev: nothing for minor %d\n", iminor(inode));
 
 	mutex_unlock(&device_list_lock);
+	unlock_kernel();
 	return status;
 }