From 1c7fcf832e03de8239a12897fb8b5767113e1b51 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Sebastian=20Dr=C3=B6ge?= <sebastian.droege@collabora.co.uk>
Date: Thu, 20 Dec 2012 14:45:18 +0100
Subject: [PATCH] omxrecmutex: Fix a small race condition when unlocking a
 non-recursive lock

---
 omx/gstomxrecmutex.c | 22 +++++++++++++++-------
 omx/gstomxrecmutex.h |  2 +-
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/omx/gstomxrecmutex.c b/omx/gstomxrecmutex.c
index 35731fb..bc4c9cb 100644
--- a/omx/gstomxrecmutex.c
+++ b/omx/gstomxrecmutex.c
@@ -29,7 +29,7 @@ gst_omx_rec_mutex_init (GstOMXRecMutex * mutex)
 {
   g_mutex_init (&mutex->lock);
   g_mutex_init (&mutex->recursion_lock);
-  mutex->recursion_allowed = FALSE;
+  g_atomic_int_set (&mutex->recursion_allowed, FALSE);
 }
 
 void
@@ -55,9 +55,13 @@ gst_omx_rec_mutex_unlock (GstOMXRecMutex * mutex)
 void
 gst_omx_rec_mutex_begin_recursion (GstOMXRecMutex * mutex)
 {
+  gboolean exchanged;
+
   g_mutex_lock (&mutex->recursion_lock);
-  g_assert (mutex->recursion_allowed == FALSE);
-  mutex->recursion_allowed = TRUE;
+  exchanged =
+      g_atomic_int_compare_and_exchange (&mutex->recursion_allowed, FALSE,
+      TRUE);
+  g_assert (exchanged);
   g_mutex_unlock (&mutex->recursion_lock);
 }
 
@@ -65,9 +69,13 @@ gst_omx_rec_mutex_begin_recursion (GstOMXRecMutex * mutex)
 void
 gst_omx_rec_mutex_end_recursion (GstOMXRecMutex * mutex)
 {
+  gboolean exchanged;
+
   g_mutex_lock (&mutex->recursion_lock);
-  g_assert (mutex->recursion_allowed == TRUE);
-  mutex->recursion_allowed = FALSE;
+  exchanged =
+      g_atomic_int_compare_and_exchange (&mutex->recursion_allowed, TRUE,
+      FALSE);
+  g_assert (exchanged);
   g_mutex_unlock (&mutex->recursion_lock);
 }
 
@@ -75,7 +83,7 @@ void
 gst_omx_rec_mutex_recursive_lock (GstOMXRecMutex * mutex)
 {
   g_mutex_lock (&mutex->recursion_lock);
-  if (!mutex->recursion_allowed) {
+  if (!g_atomic_int_get (&mutex->recursion_allowed)) {
     /* no recursion allowed, lock the proper mutex */
     g_mutex_unlock (&mutex->recursion_lock);
     g_mutex_lock (&mutex->lock);
@@ -89,7 +97,7 @@ gst_omx_rec_mutex_recursive_unlock (GstOMXRecMutex * mutex)
    * we hold at least one of the two locks and
    * either lock protects it from being changed.
    */
-  if (mutex->recursion_allowed) {
+  if (g_atomic_int_get (&mutex->recursion_allowed)) {
     g_mutex_unlock (&mutex->recursion_lock);
   } else {
     g_mutex_unlock (&mutex->lock);
diff --git a/omx/gstomxrecmutex.h b/omx/gstomxrecmutex.h
index 79c49af..4a5a0ec 100644
--- a/omx/gstomxrecmutex.h
+++ b/omx/gstomxrecmutex.h
@@ -91,7 +91,7 @@ struct _GstOMXRecMutex {
    * the recursion_lock instead of the master lock.
    * This variable is protected by both locks.
    */
-  volatile gboolean recursion_allowed;
+  volatile gint recursion_allowed;
 };
 
 void            gst_omx_rec_mutex_init (GstOMXRecMutex * mutex);
-- 
2.7.4