Helgrind causing data race warning in mutex_destroy_WRK?

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).

The conflicting access is a write to the field __data.__owner of the mutex (https://elixir.bootlin.com/glibc/glibc-2.31/source/nptl/pthread_mutex_unlock.c#L52).

Any ideas what could be going on here?

Thanks,
Adriaan