NFS: nfs_invalidate_folio() must observe the offset and size arguments

If we're truncating part of the folio, then we need to write out the
data on the part that is not covered by the cancellation.

Fixes: d47992f ("mm: change invalidatepage prototype to accept length")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

Author: Trond Myklebust

fs/nfs/file.c

@@ -475,10 +475,11 @@ static void nfs_invalidate_folio(struct folio *folio, size_t offset,
 	dfprintk(PAGECACHE, "NFS: invalidate_folio(%lu, %zu, %zu)\n",
 		 folio->index, offset, length);
 
-	if (offset != 0 || length < folio_size(folio))
-		return;
 	/* Cancel any unstarted writes on this page */
-	nfs_wb_folio_cancel(inode, folio);
+	if (offset != 0 || length < folio_size(folio))
+		nfs_wb_folio(inode, folio);
+	else
+		nfs_wb_folio_cancel(inode, folio);
 	folio_wait_private_2(folio); /* [DEPRECATED] */
 	trace_nfs_invalidate_folio(inode, folio_pos(folio) + offset, length);
 }

fs/nfs/write.c

@@ -2045,6 +2045,7 @@ int nfs_wb_folio_cancel(struct inode *inode, struct folio *folio)
 		 * release it */
 		nfs_inode_remove_request(req);
 		nfs_unlock_and_release_request(req);
+		folio_cancel_dirty(folio);
 	}
 
 	return ret;