Re: Helgrind causing data race warning in mutex_destroy_WRK?

On mardi 17 août 2021 09:59:23 CEST Schmidt, Adriaan wrote:
> Hi.
> 
> Running Helgrind (Valgrind 3.17.0) on arm32 (Linux 4.14.139), glibc 2.31,
> and an application using Poco 1.10.1, I see the following:
> 
> ==17922== Possible data race during read of size 1 at 0x64BD4C4 by thread
> #97 ==17922== Locks held: 1, at address 0x1C134CC
> ==17922==    at 0x48536D8: my_memcmp (hg_intercepts.c:220)
> ==17922==    by 0x4853BBF: mutex_destroy_WRK (hg_intercepts.c:859)
> ==17922==    by 0x48572F7: pthread_mutex_destroy (hg_intercepts.c:882)
> ==17922==    by 0x5705F23: Poco::EventImpl::~EventImpl()
> (Event_POSIX.cpp:96) ==17922==    by 0x5706393: Poco::Event::~Event()
> (Event.cpp:40)
> ==17922==    by 0x578099B: Poco::Timer::~Timer() (Timer.cpp:34)
> ==17922==    by 0x5470827: Poco::Data::SessionPool::~SessionPool()
> (SessionPool.cpp:40) ==17922==    by 0x54708A7:
> Poco::Data::SessionPool::~SessionPool() (SessionPool.cpp:50) ==.....==    [
> ... ]
> ==17922==
> ==17922== This conflicts with a previous write of size 4 by thread #7
> ==17922== Locks held: none
> ==17922==    at 0x57F8998: __pthread_mutex_unlock_usercnt
> (pthread_mutex_unlock.c:52) ==17922==    by 0x4854273: mutex_unlock_WRK
> (hg_intercepts.c:1106) ==17922==    by 0x4857337: pthread_mutex_unlock
> (hg_intercepts.c:1124) ==17922==    by 0x5781153: setImpl
> (Event_POSIX.h:61)
> ==17922==    by 0x5781153: set (Event.h:101)
> ==17922==    by 0x5781153: Poco::Timer::run() (Timer.cpp:216)
> ==17922==    by 0x577ACAF: Poco::PooledThread::run() (ThreadPool.cpp:199)
> ==17922==    by 0x57765B3: Poco::ThreadImpl::runnableEntry(void*)
> (Thread_POSIX.cpp:345) ==17922==    by 0x48562FF: mythread_wrapper
> (hg_intercepts.c:398)
> ==17922==    by 0x57F4143: start_thread (pthread_create.c:477)
> 
> To me it seems that Helgrind itself is causing the warning when calculating
> mutex_is_init (hg_intercepts.c:859).

Isn't this rather a race between unlocking a mutex and destroying that mutex?

-- 
David Faure, [email protected], http://www.davidfaure.fr
Working on KDE Frameworks 5