nfs: mark nfs_page reqs with flag for extra ref

Change the use of PG_INODE_REF - set it when taking extra reference on
subrequests and take care to only release once for each request.

Signed-off-by: Weston Andros Adamson <dros@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 98ff061..8e5745a 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -448,7 +448,9 @@
 		set_page_private(req->wb_page, (unsigned long)req);
 	}
 	nfsi->npages++;
-	set_bit(PG_INODE_REF, &req->wb_flags);
+	/* this a head request for a page group - mark it as having an
+	 * extra reference so sub groups can follow suit */
+	WARN_ON(test_and_set_bit(PG_INODE_REF, &req->wb_flags));
 	kref_get(&req->wb_kref);
 	spin_unlock(&inode->i_lock);
 }
@@ -474,7 +476,9 @@
 		nfsi->npages--;
 		spin_unlock(&inode->i_lock);
 	}
-	nfs_release_request(req);
+
+	if (test_and_clear_bit(PG_INODE_REF, &req->wb_flags))
+		nfs_release_request(req);
 }
 
 static void