CONCURRENCY.DU : Double Unlock

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CodeSonar^® 9.2p0

CONFIDENTIAL

CodeSecure Inc

C and C++

Binaries

CONCURRENCY.DU : Double Unlock

Summary

A mutex has been unlocked twice but there is no intervening lock, or is unlocked having never been locked.

For broader checking for double-unlocking phenomena, enable warning class Missing Lock Acquisition.

Properties

Class Name

Double Unlock

Significance

reliability

Mnemonic

CONCURRENCY.DU

Triggering Functions

A warning is triggered if a lock release function is called to acquire a mutex that is not currently locked: either it has never been locked or it has previously been unlocked without an intervening lock.

For the purpose of this check:

The following functions are treated as acquiring a lock.
- Any function treated as a lock acquisition function by CodeSonar:
  - any library function that is recognized as a lock acquisition function because CodeSonar ships with a library model that identifies it as such, and
  - any function for which you have added a library model identifying it as a lock acquisition function.
The following functions are treated as releasing a lock.
- Any function treated as a lock release function by CodeSonar:
  - any library function that is recognized as a lock release function because CodeSonar ships with a library model that identifies it as such, and
  - any function for which you have added a library model identifying it as a lock release function.

Example

#include <pthread.h>

void du_1(pthread_mutex_t lock){
  pthread_mutex_lock(&lock);
  pthread_mutex_unlock(&lock);
  pthread_mutex_unlock(&lock);   /* 'Double Unlock' warning issued here */
}

void du_2(pthread_mutex_t lock){
  pthread_mutex_unlock(&lock);
  pthread_mutex_lock(&lock);
  pthread_mutex_unlock(&lock);   /* 'Double Unlock' warning issued here
                                  *  - the second call to pthread_mutex_lock()
                                  *    may have failed to acquire the lock.
                                  */
}

int no_du(pthread_mutex_t lock){
  if (!pthread_mutex_unlock(&lock)){return -1;}
  if (!pthread_mutex_lock(&lock)){return -1;}
  return pthread_mutex_unlock(&lock);                          /* ok: if control reaches this line,
                                                                * the call to pthread_mutex_lock() must have succeeded
                                                                */
}

Notes

Attempting to unlock an already-unlocked mutex can lead to undefined behavior.

Relevant Configuration File Parameters

The following configuration file parameters affect checks for this warning class.

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