wrappers for ->i_mutex access

parallel to mutex_{lock,unlock,trylock,is_locked,lock_nested},
inode_foo(inode) being mutex_foo(&inode->i_mutex).

Please, use those for access to ->i_mutex; over the coming cycle
->i_mutex will become rwsem, with ->lookup() done with it held
only shared.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namespace.c b/fs/namespace.c
index a830e14..4fb1691 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1961,9 +1961,9 @@
 	struct vfsmount *mnt;
 	struct dentry *dentry = path->dentry;
 retry:
-	mutex_lock(&dentry->d_inode->i_mutex);
+	inode_lock(dentry->d_inode);
 	if (unlikely(cant_mount(dentry))) {
-		mutex_unlock(&dentry->d_inode->i_mutex);
+		inode_unlock(dentry->d_inode);
 		return ERR_PTR(-ENOENT);
 	}
 	namespace_lock();
@@ -1974,13 +1974,13 @@
 			mp = new_mountpoint(dentry);
 		if (IS_ERR(mp)) {
 			namespace_unlock();
-			mutex_unlock(&dentry->d_inode->i_mutex);
+			inode_unlock(dentry->d_inode);
 			return mp;
 		}
 		return mp;
 	}
 	namespace_unlock();
-	mutex_unlock(&path->dentry->d_inode->i_mutex);
+	inode_unlock(path->dentry->d_inode);
 	path_put(path);
 	path->mnt = mnt;
 	dentry = path->dentry = dget(mnt->mnt_root);
@@ -1992,7 +1992,7 @@
 	struct dentry *dentry = where->m_dentry;
 	put_mountpoint(where);
 	namespace_unlock();
-	mutex_unlock(&dentry->d_inode->i_mutex);
+	inode_unlock(dentry->d_inode);
 }
 
 static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp)