(Merge 3.3) Issue #18343: faulthandler.register() now keeps the previous signal

handler when the function is called twice, so faulthandler.unregister()
restores correctly the original signal handler.

Misc/NEWS

@@ -138,6 +138,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #18343: faulthandler.register() now keeps the previous signal handler
+  when the function is called twice, so faulthandler.unregister() restores
+  correctly the original signal handler.
+
 - Issue #17097: Make multiprocessing ignore EINTR.
 
 - Issue #18339: Negative ints keys in unpickler.memo dict no longer cause a

Modules/faulthandler.c

@@ -741,6 +741,8 @@ faulthandler_register_py(PyObject *self,
             PyErr_SetFromErrno(PyExc_OSError);
             return NULL;
         }
+
+        user->previous = previous;
     }
 
     Py_XDECREF(user->file);
@@ -749,7 +751,6 @@ faulthandler_register_py(PyObject *self,
     user->fd = fd;
     user->all_threads = all_threads;
     user->chain = chain;
-    user->previous = previous;
     user->interp = tstate->interp;
     user->enabled = 1;