From fb11664cb710841df0fe2ff06db745f9566b6010 Mon Sep 17 00:00:00 2001
From: Victor Stinner <victor.stinner@gmail.com>
Date: Mon, 26 Jun 2017 15:41:42 +0200
Subject: [PATCH] bpo-30703: More reentrant signal handler

Modify the signal handler to not call Py_AddPendingCall() function
since this function uses a lock and a list, and so is unlikely to be
reentrant. Add a new _PyEval_SignalReceived() function which only
writes into an atomic variable and so is reentrant.
---
 Include/ceval.h        |  1 +
 Modules/signalmodule.c |  2 +-
 Python/ceval.c         | 15 +++++++++++++++
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/Include/ceval.h b/Include/ceval.h
index e5cb4112274794..b2d57cbd6f7425 100644
--- a/Include/ceval.h
+++ b/Include/ceval.h
@@ -54,6 +54,7 @@ PyAPI_FUNC(int) PyEval_MergeCompilerFlags(PyCompilerFlags *cf);
 #endif
 
 PyAPI_FUNC(int) Py_AddPendingCall(int (*func)(void *), void *arg);
+PyAPI_FUNC(void) _PyEval_SignalReceived(void);
 PyAPI_FUNC(int) Py_MakePendingCalls(void);
 
 /* Protection against deeply nested recursive calls
diff --git a/Modules/signalmodule.c b/Modules/signalmodule.c
index 75abc98bc4b593..957ab54b652f13 100644
--- a/Modules/signalmodule.c
+++ b/Modules/signalmodule.c
@@ -248,7 +248,7 @@ trip_signal(int sig_num)
         /* Set is_tripped after setting .tripped, as it gets
            cleared in PyErr_CheckSignals() before .tripped. */
         is_tripped = 1;
-        Py_AddPendingCall(checksignals_witharg, NULL);
+        _PyEval_SignalReceived();
     }
 
     /* And then write to the wakeup fd *after* setting all the globals and
diff --git a/Python/ceval.c b/Python/ceval.c
index 3243a4f8a01d9c..317b088eb1d853 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -387,6 +387,15 @@ Py_AddPendingCall(int (*func)(void *), void *arg)
     return result;
 }
 
+void
+_PyEval_SignalReceived(void)
+{
+    /* bpo-30703: Function called when the C signal handler of Python gets a
+       signal. We cannot queue a callback using Py_AddPendingCall() since this
+       function is not reentrant (use a lock and a list). */
+    SIGNAL_PENDING_CALLS();
+}
+
 int
 Py_MakePendingCalls(void)
 {
@@ -394,6 +403,12 @@ Py_MakePendingCalls(void)
     int i;
     int r = 0;
 
+    /* Python signal handler doesn't really queue a callback: it only signals
+       that an UNIX signal was received, see _PyEval_SignalReceived(). */
+    if (PyErr_CheckSignals() < 0) {
+        return -1;
+    }
+
     if (!pending_lock) {
         /* initial allocation of the lock */
         pending_lock = PyThread_allocate_lock();