misc: cdev lock_kernel() pushdown

misc_open() looks fine, but who knows what all of the misc drivers are
doing in their open() functions?
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

drivers/char/misc.c

@@ -49,6 +49,7 @@
 #include <linux/device.h>
 #include <linux/tty.h>
 #include <linux/kmod.h>
+#include <linux/smp_lock.h>
 
 /*
  * Head entry for the doubly linked miscdevice list
@@ -118,6 +119,7 @@ static int misc_open(struct inode * inode, struct file * file)
 	int err = -ENODEV;
 	const struct file_operations *old_fops, *new_fops = NULL;
 	
+	lock_kernel();
 	mutex_lock(&misc_mtx);
 	
 	list_for_each_entry(c, &misc_list, list) {
@@ -155,6 +157,7 @@ static int misc_open(struct inode * inode, struct file * file)
 	fops_put(old_fops);
 fail:
 	mutex_unlock(&misc_mtx);
+	unlock_kernel();
 	return err;
 }