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From caa6f1ea462d0f0c612b871106e3e309fe0290f5 Mon Sep 17 00:00:00 2001
From: Stephan Bergmann <sbergman@redhat.com>
Date: Thu, 16 Aug 2018 09:04:35 +0200
Subject: [PATCH] Handle race between ExceptionHandler::SignalHandler and
 ~ExceptionHandler

...where thread A is blocked locking g_handler_stack_mutex_ in SignalHandler
while thread B executes ~ExceptionHandler and sets g_handler_stack to null, but
which thread A didn't expect to be null once it acquired the lock.
---
 src/client/linux/handler/exception_handler.cc | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/client/linux/handler/exception_handler.cc b/src/client/linux/handler/exception_handler.cc
index b895f6d7..4d58e510 100644
--- a/src/client/linux/handler/exception_handler.cc
+++ b/src/client/linux/handler/exception_handler.cc
@@ -372,8 +372,10 @@ void ExceptionHandler::SignalHandler(int sig, siginfo_t* info, void* uc) {
   }
 
   bool handled = false;
-  for (int i = g_handler_stack_->size() - 1; !handled && i >= 0; --i) {
-    handled = (*g_handler_stack_)[i]->HandleSignal(sig, info, uc);
+  if (g_handler_stack_ != NULL) {
+    for (int i = g_handler_stack_->size() - 1; !handled && i >= 0; --i) {
+      handled = (*g_handler_stack_)[i]->HandleSignal(sig, info, uc);
+    }
   }
 
   // Upon returning from this signal handler, sig will become unmasked and then
-- 
2.17.1