embedded assertion_error ai_generated true

FreeRTOS: xSemaphoreTakeRecursive failed on mutex 0x2000A000, mutex already taken by same task

ID: embedded/freertos-mutex-recursive-take

Also available as: JSON · Markdown · 中文
90%Fix Rate
89%Confidence
1Evidence
2024-11-01First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
FreeRTOS v10.5.1 active — — —
ARM GCC v12.2.1 active — — —

Root Cause

A recursive mutex was taken by a task that already holds it without a corresponding recursive give, exhausting the nesting count.

generic

中文

一个递归互斥锁被已持有它的任务获取，而没有相应的递归释放，耗尽了嵌套计数。

Official Documentation

https://www.freertos.org/a00122.html

Workarounds

  1. 95% success Ensure every xSemaphoreTakeRecursive is paired with an equal number of xSemaphoreGiveRecursive calls. Use a debug macro to track nesting count. 
    Ensure every xSemaphoreTakeRecursive is paired with an equal number of xSemaphoreGiveRecursive calls. Use a debug macro to track nesting count.
  2. 85% success Refactor code to avoid recursive mutex acquisition by using a single entry point that acquires the mutex once and calls nested functions without re-acquiring. 
    Refactor code to avoid recursive mutex acquisition by using a single entry point that acquires the mutex once and calls nested functions without re-acquiring.

中文步骤

  1. Ensure every xSemaphoreTakeRecursive is paired with an equal number of xSemaphoreGiveRecursive calls. Use a debug macro to track nesting count.
  2. Refactor code to avoid recursive mutex acquisition by using a single entry point that acquires the mutex once and calls nested functions without re-acquiring.

Dead Ends

Common approaches that don't work:

  1. Replace recursive mutex with a standard mutex 90% fail

    A standard mutex will cause a deadlock if the same task tries to take it again, as it does not support recursive acquisition.

  2. Increase the configMAX_RECURSIVE_MUTEX_DEPTH value 60% fail

    The depth is limited by task stack and memory; increasing it may mask the underlying nesting bug, leading to stack overflow later.

  3. Add a delay before taking the mutex again 80% fail

    Does not resolve the logic error; the mutex is already held, so delay only wastes CPU cycles without fixing the nesting count.