Issue #21090: io.FileIO.readall() does not ignore I/O errors anymore. Before,

it ignored I/O errors if at least the first C call read() succeed.

Misc/NEWS

@@ -27,6 +27,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #21090: io.FileIO.readall() does not ignore I/O errors anymore. Before,
+  it ignored I/O errors if at least the first C call read() succeed.
+
 - Issue #21781: ssl.RAND_add() now supports strings longer than 2 GB.
 
 - Issue #11453: asyncore: emit a ResourceWarning when an unclosed file_wrapper

Modules/_io/fileio.c

@@ -691,9 +691,9 @@ fileio_readall(fileio *self)
                 }
                 continue;
             }
-            if (bytes_read > 0)
-                break;
             if (errno == EAGAIN) {
+                if (bytes_read > 0)
+                    break;
                 Py_DECREF(result);
                 Py_RETURN_NONE;
             }