staging: vme: use image mutex for ioctl()

This implements more granular locking in vme_user_ioctl() by using separate
locks for each devfs device.

This also provides a synchronization between vme_user_read(), vme_user_write()
and vme_user_ioctl().
Signed-off-by: Dmitry Kalinkin <dmitry.kalinkin@gmail.com>
Cc: Martyn Welch <martyn.welch@ge.com>
Cc: Igor Alekseev <igor.alekseev@itep.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vme/devices/vme_user.c

@@ -41,7 +41,6 @@
 
 #include "vme_user.h"
 
-static DEFINE_MUTEX(vme_user_mutex);
 static const char driver_name[] = "vme_user";
 
 static int bus[VME_USER_BUS_MAX];
@@ -555,10 +554,12 @@ static long
 vme_user_unlocked_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
 	int ret;
+	struct inode *inode = file_inode(file);
+	unsigned int minor = MINOR(inode->i_rdev);
 
-	mutex_lock(&vme_user_mutex);
-	ret = vme_user_ioctl(file_inode(file), file, cmd, arg);
-	mutex_unlock(&vme_user_mutex);
+	mutex_lock(&image[minor].mutex);
+	ret = vme_user_ioctl(inode, file, cmd, arg);
+	mutex_unlock(&image[minor].mutex);
 
 	return ret;
 }