From 9d4a92003c8e4ba37aa7ac6b62c1487461538f53 Mon Sep 17 00:00:00 2001
From: Ludwig Ortmann <ludwig.ortmann@fu-berlin.de>
Date: Fri, 16 May 2014 15:48:48 +0200
Subject: [PATCH] core/hwtimer: disable interrupts in hwtimer_remove

Before only the hardware timer's own interrupt was being disabled.
This led to a race condition in the following scenario:

```
Thread1:
    hwtimer_remove()
    hwtimer_arch_disable_interrupt();

// INTERRUPT -> Thread2 (which has a higher priority than Thread1) gets scheduled

Thread2:
    ...
    hwtimer_remove()
    hwtimer_arch_disable_interrupt(); // hwtimer interrupt is already disabled
    ...
    hwtimer_arch_enable_interrupt();
    ...
   // yield | terminate -> Thread1 gets scheduled again

Thread1:
    ... // these instructions are being run with the hwtimer interrupt enabled
    hwtimer_arch_enable_interrupt(); // hwtimer interrupt is already enabled
```

Fixes #924
---
 core/hwtimer.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/core/hwtimer.c b/core/hwtimer.c
index b0ba36412c9e..bc0bc6c50272 100644
--- a/core/hwtimer.c
+++ b/core/hwtimer.c
@@ -202,7 +202,8 @@ int hwtimer_set_absolute(unsigned long offset, void (*callback)(void*), void *pt
 int hwtimer_remove(int n)
 {
     DEBUG("hwtimer_remove n=%d\n", n);
-    hwtimer_arch_disable_interrupt();
+
+    int state = disableIRQ();
     hwtimer_arch_unset(n);
 
     lifo_insert(lifo, n);
@@ -210,6 +211,7 @@ int hwtimer_remove(int n)
 
     lpm_prevent_sleep--;
 
-    hwtimer_arch_enable_interrupt();
+    restoreIRQ(state);
+
     return 1;
 }