new helper: ihold()

Clones an existing reference to inode; caller must already hold one.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index e1e7b96..80b35ff 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -769,7 +769,7 @@
 
 	inode = dentry->d_inode;
 	if (inode)
-		atomic_inc(&inode->i_count);
+		ihold(inode);
 	err = mnt_want_write(ipc_ns->mq_mnt);
 	if (err)
 		goto out_err;