NFS: Don't clear PG_writeback until after we've processed unstable writes

Ensure that we don't release the PG_writeback lock until after the page has
either been redirtied, or queued on the nfs_inode 'commit' list.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/nfs/write.c

@@ -920,8 +920,8 @@ static int nfs_flush_multi(struct inode *inode, struct list_head *head, int how)
 		list_del(&data->pages);
 		nfs_writedata_release(data);
 	}
-	nfs_end_page_writeback(req->wb_page);
 	nfs_redirty_request(req);
+	nfs_end_page_writeback(req->wb_page);
 	nfs_clear_page_writeback(req);
 	return -ENOMEM;
 }
@@ -966,8 +966,8 @@ static int nfs_flush_one(struct inode *inode, struct list_head *head, int how)
 	while (!list_empty(head)) {
 		struct nfs_page *req = nfs_list_entry(head->next);
 		nfs_list_remove_request(req);
-		nfs_end_page_writeback(req->wb_page);
 		nfs_redirty_request(req);
+		nfs_end_page_writeback(req->wb_page);
 		nfs_clear_page_writeback(req);
 	}
 	return -ENOMEM;
@@ -1002,8 +1002,8 @@ static int nfs_flush_list(struct inode *inode, struct list_head *head, int npage
 	while (!list_empty(head)) {
 		req = nfs_list_entry(head->next);
 		nfs_list_remove_request(req);
-		nfs_end_page_writeback(req->wb_page);
 		nfs_redirty_request(req);
+		nfs_end_page_writeback(req->wb_page);
 		nfs_clear_page_writeback(req);
 	}
 	return error;