zyfeier commented on code in PR #14465:
URL: https://github.com/apache/nuttx/pull/14465#discussion_r1812531878
##########
sched/semaphore/sem_post.c:
##########
@@ -217,3 +214,60 @@ int nxsem_post(FAR sem_t *sem)
return OK;
}
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: nxsem_post
+ *
+ * Description:
+ * When a kernel thread has finished with a semaphore, it will call
+ * nxsem_post(). This function unlocks the semaphore referenced by sem
+ * by performing the semaphore unlock operation on that semaphore.
+ *
+ * If the semaphore value resulting from this operation is positive, then
+ * no tasks were blocked waiting for the semaphore to become unlocked; the
+ * semaphore is simply incremented.
+ *
+ * If the value of the semaphore resulting from this operation is zero,
+ * then one of the tasks blocked waiting for the semaphore shall be
+ * allowed to return successfully from its call to nxsem_wait().
+ *
+ * Input Parameters:
+ * sem - Semaphore descriptor
+ *
+ * Returned Value:
+ * This is an internal OS interface and should not be used by applications.
+ * It follows the NuttX internal error return policy: Zero (OK) is
+ * returned on success. A negated errno value is returned on failure.
+ *
+ * Assumptions:
+ * This function may be called from an interrupt handler.
+ *
+ ****************************************************************************/
+
+int nxsem_post(FAR sem_t *sem)
+{
+ DEBUGASSERT(sem != NULL);
+
+ /* If this is a mutex, we can try to unlock the mutex in fast mode,
+ * else try to get it in slow mode.
+ */
+
+#if !defined(CONFIG_PRIORITY_INHERITANCE) && !defined(CONFIG_PRIORITY_PROTECT)
+ if (sem->flags & SEM_TYPE_MUTEX)
Review Comment:
If the atomic operation for count is implemented in the lib mutex, when
mutex_lock is called, it may exit early due to fast_lock, which can result in
the sem->count value not being updated. This, in turn, can cause mutex_unlock
to fail.
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