Provide a sanity check during PyThreadState_DeleteCurrent() and

PyThreadState_Delete() to avoid an infinite loop when the tstate list
is messed up and has somehow becomes circular and does not contain the
current thread.

I don't know how this happens but it does, *very* rarely.  On more than
one hardware platform.  I have not been able to reproduce it manually.

Attaching to a process where its happening: it has always been in an
infinite loop over a single element tstate list that is not the tstate
we're looking to delete.  It has been in t_bootstrap()'s call to
PyThreadState_DeleteCurrent() as a pthread is exiting.

diff --git a/Python/pystate.c b/Python/pystate.c
index 086789d3553cc909cd70fe60a880c4611153300e..36b06d67af7c2bcb7a2623403102ed456ff96e65 100644 (file)
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -240,6 +240,7 @@ tstate_delete_common(PyThreadState *tstate)
 {
        PyInterpreterState *interp;
        PyThreadState **p;
+       PyThreadState *prev_p = NULL;
        if (tstate == NULL)
                Py_FatalError("PyThreadState_Delete: NULL tstate");
        interp = tstate->interp;
@@ -252,6 +253,15 @@ tstate_delete_common(PyThreadState *tstate)
                                "PyThreadState_Delete: invalid tstate");
                if (*p == tstate)
                        break;
+               if (*p == prev_p)
+                       Py_FatalError(
+                               "PyThreadState_Delete: small circular list(!)"
+                                " and tstate not found.");
+               prev_p = *p;
+               if ((*p)->next == interp->tstate_head)
+                       Py_FatalError(
+                               "PyThreadState_Delete: circular list(!) and"
+                                " tstate not found.");
        }
        *p = tstate->next;
        HEAD_UNLOCK();