devcgroup_inode_permission: take "is it a device node" checks to inlined wrapper

inode_permission() calls devcgroup_inode_permission() and almost all such
calls are _not_ for device nodes; let's at least keep the common path
straight...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/device_cgroup.h

@@ -2,8 +2,16 @@
 #include <linux/fs.h>
 
 #ifdef CONFIG_CGROUP_DEVICE
-extern int devcgroup_inode_permission(struct inode *inode, int mask);
+extern int __devcgroup_inode_permission(struct inode *inode, int mask);
 extern int devcgroup_inode_mknod(int mode, dev_t dev);
+static inline int devcgroup_inode_permission(struct inode *inode, int mask)
+{
+	if (likely(!inode->i_rdev))
+		return 0;
+	if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
+		return 0;
+	return __devcgroup_inode_permission(inode, mask);
+}
 #else
 static inline int devcgroup_inode_permission(struct inode *inode, int mask)
 { return 0; }

security/device_cgroup.c

@@ -474,17 +474,11 @@ struct cgroup_subsys devices_subsys = {
 	.subsys_id = devices_subsys_id,
 };
 
-int devcgroup_inode_permission(struct inode *inode, int mask)
+int __devcgroup_inode_permission(struct inode *inode, int mask)
 {
 	struct dev_cgroup *dev_cgroup;
 	struct dev_whitelist_item *wh;
 
-	dev_t device = inode->i_rdev;
-	if (!device)
-		return 0;
-	if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
-		return 0;
-
 	rcu_read_lock();
 
 	dev_cgroup = task_devcgroup(current);