mutex held in a thread which is cancelled stays busy

[Erich Dollansky]

Hi,

On Tue, 6 Aug 2019 23:38:51 -0400
Daniel Eischen <deischen at freebsd.org> wrote:

> > On Aug 6, 2019, at 9:55 PM, Erich Dollansky
> > <freebsd.ed.lists at sumeritec.com> wrote:
> > 
> > Hi,
> > 
> > On Tue, 6 Aug 2019 20:58:30 -0400
> > Daniel Eischen <deischen at freebsd.org> wrote:
> >   
> >>> On Aug 6, 2019, at 4:54 AM, Erich Dollansky
> >>> <freebsd.ed.lists at sumeritec.com> wrote:
> >>> 
> >>> Hi,
> >>> 
> >>> for testing purpose, I did the following.
> >>> 
> >>> Start a thread, initialise a mutex in a global variable, lock the
> >>> mutex and wait in that thread.
> >>> 
> >>> Wait in the main program until above's thread waits and cancel it.
> >>> 
> >>> Clean up behind the cancelled thread but leave intentional the
> >>> mutex locked.
> >>> 
> >>> I would have expected now to get an error like 'EOWNERDEAD' doing
> >>> operations with that mutex. But I get 'EBUSY' as the error.    
> >> 
> >> Are you initializing the mutex as a robust mutex, via
> >> pthread_mutexattr_setrobust()?  Are you using _lock() or
> >> _trylock()?
> >> 
> >> For _trylock(), you only get EOWNERDEAD for robust mutexes.  It
> >> seems that you should get EOWNERDEAD for _lock() in this case, so
> >> if that's what you're doing, it sounds like it might be a bug.
> >>   
> > I did both. One time with initialising the mutex with its defaults
> > by handing over NULL as the attribute setting and one time with the
> > attributes set.
> > 
> > I use this line to set the attribute:
> > 
> > pres = pthread_mutexattr_setrobust (& Attr, PTHREAD_MUTEX_ROBUST);
> > 
> > The following line:
> > 
> > pthread_mutexattr_getrobust (& Attr, &pres);
> > 
> > Sets pres also to 1.
> > 
> > I am doing this on 12.0-STABLE FreeBSD 12.0-STABLE r350391 GENERIC
> > amd64 with the systems standard compiler.
> > 
> > Is this the corrent way of doing it?  
> 
> Yes, I believe so.  I'm curious if the bug also exists in -current.
> 
I do not have CURRENT on any machine at the moment.

Erich