[src] bug fix in ipc.c (#7972)

Signed-off-by: Shell <smokewood@qq.com>

src/ipc.c

@@ -956,8 +956,14 @@ void rt_mutex_drop_thread(rt_mutex_t mutex, rt_thread_t thread)
 
     rt_list_remove(&(thread->tlist));
 
-    /* should change the priority of mutex owner thread */
-    if (mutex->owner->current_priority == thread->current_priority)
+    /**
+     * Should change the priority of mutex owner thread
+     * Note: After current thread is detached from mutex pending list, there is
+     *       a chance that the mutex owner has been released the mutex. Which
+     *       means mutex->owner can be NULL at this point. If that happened,
+     *       it had already reset its priority. So it's okay to skip
+     */
+    if (mutex->owner && mutex->owner->current_priority == thread->current_priority)
         need_update = RT_TRUE;
 
     /* update the priority of mutex */
@@ -1304,8 +1310,14 @@ static rt_err_t _rt_mutex_take(rt_mutex_t mutex, rt_int32_t timeout, int suspend
 
                     rt_bool_t need_update = RT_FALSE;
 
-                    /* should change the priority of mutex owner thread */
-                    if (mutex->owner->current_priority == thread->current_priority)
+                    /**
+                     * Should change the priority of mutex owner thread
+                     * Note: After current thread is detached from mutex pending list, there is
+                     *       a chance that the mutex owner has been released the mutex. Which
+                     *       means mutex->owner can be NULL at this point. If that happened,
+                     *       it had already reset its priority. So it's okay to skip
+                     */
+                    if (mutex->owner && mutex->owner->current_priority == thread->current_priority)
                         need_update = RT_TRUE;
 
                     /* update the priority of mutex */
@@ -1340,8 +1352,12 @@ static rt_err_t _rt_mutex_take(rt_mutex_t mutex, rt_int32_t timeout, int suspend
                     /* enable interrupt */
                     rt_hw_interrupt_enable(level);
 
-                    /* return error */
-                    return thread->error;
+                    /* clear pending object before exit */
+                    thread->pending_object = RT_NULL;
+
+                    /* fix thread error number to negative value and return */
+                    ret = thread->error;
+                    return ret > 0 ? -ret : ret;
                 }
             }
         }