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>

fs/overlayfs/dir.c

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 692ceda..ed95272 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -167,7 +167,7 @@
 	struct dentry *newdentry;
 	int err;
 
-	mutex_lock_nested(&udir->i_mutex, I_MUTEX_PARENT);
+	inode_lock_nested(udir, I_MUTEX_PARENT);
 	newdentry = lookup_one_len(dentry->d_name.name, upperdir,
 				   dentry->d_name.len);
 	err = PTR_ERR(newdentry);
@@ -185,7 +185,7 @@
 out_dput:
 	dput(newdentry);
 out_unlock:
-	mutex_unlock(&udir->i_mutex);
+	inode_unlock(udir);
 	return err;
 }
 
@@ -258,9 +258,9 @@
 	if (err)
 		goto out_cleanup;
 
-	mutex_lock(&opaquedir->d_inode->i_mutex);
+	inode_lock(opaquedir->d_inode);
 	err = ovl_set_attr(opaquedir, &stat);
-	mutex_unlock(&opaquedir->d_inode->i_mutex);
+	inode_unlock(opaquedir->d_inode);
 	if (err)
 		goto out_cleanup;
 
@@ -599,7 +599,7 @@
 	struct dentry *upper = ovl_dentry_upper(dentry);
 	int err;
 
-	mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
+	inode_lock_nested(dir, I_MUTEX_PARENT);
 	err = -ESTALE;
 	if (upper->d_parent == upperdir) {
 		/* Don't let d_delete() think it can reset d_inode */
@@ -619,7 +619,7 @@
 	 * now.
 	 */
 	d_drop(dentry);
-	mutex_unlock(&dir->i_mutex);
+	inode_unlock(dir);
 
 	return err;
 }