changer: BKL pushdown

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

drivers/scsi/ch.c

@@ -22,6 +22,7 @@
 #include <linux/chio.h>			/* here are all the ioctls */
 #include <linux/mutex.h>
 #include <linux/idr.h>
+#include <linux/smp_lock.h>
 
 #include <scsi/scsi.h>
 #include <scsi/scsi_cmnd.h>
@@ -571,16 +572,19 @@ ch_open(struct inode *inode, struct file *file)
 	scsi_changer *ch;
 	int minor = iminor(inode);
 
+	lock_kernel();
 	spin_lock(&ch_index_lock);
 	ch = idr_find(&ch_index_idr, minor);
 
 	if (NULL == ch || scsi_device_get(ch->device)) {
 		spin_unlock(&ch_index_lock);
+		unlock_kernel();
 		return -ENXIO;
 	}
 	spin_unlock(&ch_index_lock);
 
 	file->private_data = ch;
+	unlock_kernel();
 	return 0;
 }