Just a quick note to say thanks! I did not know that. I thought xSemaphoreGive() would return pdFAIL for that case. And two of my own APIs were affected. My functions spi_close() and i2c_close() are written to tolerate a user calling them unnecessarily. I had comments in each one that said “we don’t need to bother verifying that the current task is the mutex owner since FreeRTOS verifies that for us”. Oops!