🐛 Fix race and an abandoned mutex (#180)

NOTE: CI build fails only due to what I assume is a plumbing issue. Inspecting the logs reveals that everything compiles correctly.

* Added volatile loads and fixed an abondoned mutex

* Moved early out earlier

* Fix indent

* Fix understanding of memory model

* Fix indentation

* Fix side of memory barrier

* Fix warning

src/display/lv_misc/lv_task.c

@@ -63,17 +63,27 @@ void lv_task_init(void)
 LV_ATTRIBUTE_TASK_HANDLER void lv_task_handler(void)
 {
     LV_LOG_TRACE("lv_task_handler started");
+    bool task_run = __atomic_load_n(&lv_task_run, __ATOMIC_ACQUIRE);
+
+    if(task_run == false)
+    {
+        LV_LOG_TRACE("lv_task_handler bailed early, task run false");
+        return;
+    }
 
     /*Avoid concurrent running of the task handler*/
     static bool task_handler_mutex = false;
-    if(task_handler_mutex) return;
-    task_handler_mutex = true;
+
+    bool expected = false;
+    bool toSet = true;
+    bool alreadyTaken = __atomic_compare_exchange(&task_handler_mutex, &expected, &toSet,/* weak*/ false, __ATOMIC_ACQUIRE, __ATOMIC_ACQUIRE);
+
+    if (alreadyTaken) return;
 
     static uint32_t idle_period_start = 0;
     static uint32_t handler_start = 0;
     static uint32_t busy_time = 0;
 
-    if(lv_task_run == false) return;
 
     handler_start = lv_tick_get();
 
@@ -148,7 +158,7 @@ LV_ATTRIBUTE_TASK_HANDLER void lv_task_handler(void)
 
     }
 
-    task_handler_mutex = false;     /*Release the mutex*/
+    __atomic_store_n(&task_handler_mutex, false, __ATOMIC_RELEASE);
 
     LV_LOG_TRACE("lv_task_handler ready");
 }
@@ -284,7 +294,7 @@ void lv_task_reset(lv_task_t * lv_task_p)
  */
 void lv_task_enable(bool en)
 {
-    lv_task_run = en;
+    __atomic_store_n(&lv_task_run, en, __ATOMIC_RELAXED);
 }
 
 /**