> -----Original Message-----
> From: Jan Kiszka <jan.kis...@siemens.com>
> Sent: Dienstag, 21. Jänner 2020 18:46
> To: Lange Norbert <norbert.la...@andritz.com>; Xenomai
> (xenomai@xenomai.org) <xenomai@xenomai.org>
> Subject: Re: Cobalt deadlock for no apparent reason
>
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> ATTACHMENTS.
>
>
> On 20.01.20 19:03, Lange Norbert via Xenomai wrote:
> > Hello,
> >
> > I got a deadlock while running through gdbserver, this is an
> > implementation of a synchronized queue, Fup side waits via condition
> variable, main wants to push data, but main fails to acquire the mutex.
> > The mutex is an errorchecking type, without priority inheritance, and not
> used elsewhere.
> >
> >
> > The task are as following:
> >
> > CPU PID CLASS TYPE PRI TIMEOUT STAT NAME
> > 1 1686 rt cobalt 4 - Wt main
> > 3 1690 rt cobalt 2 - Wt fup.medium
> >
> > main is stuck in this function
> >
> > int mutex_lock(struct mutex_data *pData) {
> > pthread_t threadId = pthread_self();
> > // assert(pthread_equal(threadId, pData->m_LockId) == 0);
> > -> int r = pthread_mutex_lock(&pData->m_Mutex);
> > assert(r == 0);
> > pData->m_LockId = threadId;
> > return r;
> > }
> >
> > In libcobalt:
> > do
> > ret = XENOMAI_SYSCALL1(sc_cobalt_mutex_lock, _mutex);
> > while (ret == -EINTR);
> >
> > fup.medium is stuck in:
> >
> > int conditionvar_wait(struct conditionvar_data *pData, struct
> > mutex_data *pMutex) {
> > pthread_t sid = pthread_self();
> > assert(pthread_equal(sid, pMutex->m_LockId) != 0);
> > pMutex->m_LockId = 0;
> > -> int r = pthread_cond_wait(&pData->m_CondVar, &pMutex-
> >m_Mutex);
> > assert(r == 0);
> > pMutex->m_LockId = sid;
> > return r;
> > }
> >
> > In libcobalt:
> > while (err == -EINTR)
> > err = XENOMAI_SYSCALL2(sc_cobalt_cond_wait_epilogue, _cnd, _mx);
> >
>
> This is likely tricky to debug by just looking at things. Can you factor out a
> reproducer?
Well, the "no apparent reason" is key here, it's not easily reproducible either.
Might help if you tell me how I could end up in this situation, AFAIK the
pthread_cond_wait function got an interrupt,
when can this occur for example.
It seems limited to running under a debugger (or just happens a lot less
without), and when the process dlopen's libraries this pauses
the process for example. At that time the fup.medium is supposed to stick in
pthread_cond_wait (means the dlopens might cause spurious wakeups)
and notified after everything is ready to run.
So, if you have any idea how I could narrow it down, I migh be able to build a
reproducer. Right now I am going to use a timed mutex to atleast detect the
issue.
Norbert
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