MTX Lock implementation question

[John Baldwin]

On Wednesday 04 March 2009 12:34:40 pm Barney Cordoba wrote:
> 
> --- On Wed, 3/4/09, John Baldwin <jhb at freebsd.org> wrote:
> 
> > From: John Baldwin <jhb at freebsd.org>
> > Subject: Re: MTX Lock implementation question
> > To: freebsd-current at freebsd.org, barney_cordoba at yahoo.com
> > Cc: current at freebsd.org
> > Date: Wednesday, March 4, 2009, 10:13 AM
> > On Wednesday 04 March 2009 7:54:32 am Barney Cordoba wrote:
> > > 
> > > Suppose the following:
> > > 
> > > Module foo.c
> > > 
> > > foo_getlock(sc)
> > > {
> > >    FOO_LOCK(sc);
> > > }
> > > foo_unlock(sc)
> > > {
> > >    FOO_UNLOCK(sc);
> > > }
> > > foo_dosomething(sc)
> > > {
> > >    MTX_LOCK_ASSERT(sc);
> > >    foo_dooit();
> > > }
> > > 
> > > Module bar.c
> > > 
> > > bar_dofoo()
> > > {
> > >    foo_getlock(sc);
> > >    foo_dosomething(sc);
> > >    foo_unlock(sc);
> > > }
> > 
> > This works fine.
> >  
> > > Is this something that shouldn't work? I need to
> > access functions
> > >  that require locks in a different module, but this
> > code barfs on 
> > > ASSERT with witness enabled. Is this a deflugalty in
> > WITNESS, or do 
> > > I need to create functions within foo that do the
> > locking? Its been
> > > working ok for awhile (its not a high volume function)
> > but when I 
> > > fired up witness to debug something else I encountered
> > witness panics.
> > 
> > You probably have a real bug that WITNESS is warning about
> > however.
> > 
> > -- 
> > John Baldwin
> 
> It seems that theres a problem when the mutex is initialized with a type
> of NULL. Changing it to a non-null string eliminated the issue. I'm
> running a 7.0 base system.

Hmm, mutexes are required to be named.  The "type" argument is optional, but 
the name is not.  So you can't do:

	mtx_init(&m, NULL, NULL, MTX_DEF);


You can, however do:

	mtx_init(&m, "foo", NULL, MTX_DEF);

-- 
John Baldwin