nfs: fix error handling in lock_and_join_requests

commit 94970014 upstream.

This fixes handling of errors from nfs_page_group_lock in
nfs_lock_and_join_requests.  It now releases the inode lock and the
reference to the head request.
Reported-by: Peng Tao <tao.peng@primarydata.com>
Signed-off-by: Weston Andros Adamson <dros@primarydata.com>
Reviewed-by: Peng Tao <tao.peng@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/nfs/write.c

@@ -455,8 +455,11 @@ nfs_lock_and_join_requests(struct page *page, bool nonblock)
 
 	/* lock each request in the page group */
 	ret = nfs_page_group_lock(head, true);
-	if (ret < 0)
+	if (ret < 0) {
+		spin_unlock(&inode->i_lock);
+		nfs_release_request(head);
 		return ERR_PTR(ret);
+	}
 	subreq = head;
 	do {
 		/*