nfs: check wait_on_bit_lock err in page_group_lock

Return errors from wait_on_bit_lock from nfs_page_group_lock.

Add a bool argument @wait to nfs_page_group_lock. If true, loop over
wait_on_bit_lock until it returns cleanly. If false, return the error
from wait_on_bit_lock.

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 d357728..8d1ed2b 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -216,7 +216,7 @@
 	unsigned int pos = 0;
 	unsigned int len = nfs_page_length(req->wb_page);
 
-	nfs_page_group_lock(req);
+	nfs_page_group_lock(req, true);
 
 	do {
 		tmp = nfs_page_group_search_locked(req->wb_head, pos);
@@ -456,7 +456,9 @@
 	}
 
 	/* lock each request in the page group */
-	nfs_page_group_lock(head);
+	ret = nfs_page_group_lock(head, false);
+	if (ret < 0)
+		return ERR_PTR(ret);
 	subreq = head;
 	do {
 		/*