From f612475c997dee0e23805bb7982ec3e820546f02 Mon Sep 17 00:00:00 2001
From: Alexander Boettcher <alexander.boettcher@genode-labs.com>
Date: Fri, 22 Jun 2012 14:46:39 +0200
Subject: [PATCH] Bug fix: null ptr dereference in base/semaphore

If nobody is blocked in a semaphore, nothing can be dequeued. If
the semaphore is used for signalling, there can be somebody in the queue,
but not necessarily.
---
 base/include/base/semaphore.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/base/include/base/semaphore.h b/base/include/base/semaphore.h
index 85b7fbef1a..fe87eccdd4 100644
--- a/base/include/base/semaphore.h
+++ b/base/include/base/semaphore.h
@@ -128,7 +128,9 @@ namespace Genode {
 				 * Remove element from queue and wake up the corresponding
 				 * blocking thread
 				 */
-				_queue.dequeue()->wake_up();
+				Semaphore_queue::Element * element = _queue.dequeue();
+				if (element)
+					element->wake_up();
 			}
 
 			void down()