Date: Wed, 4 Mar 2009 13:05:54 -0500 From: John Baldwin <jhb@freebsd.org> To: barney_cordoba@yahoo.com Cc: current@freebsd.org Subject: Re: MTX Lock implementation question Message-ID: <200903041305.54726.jhb@freebsd.org> In-Reply-To: <415008.75717.qm@web63902.mail.re1.yahoo.com> References: <415008.75717.qm@web63902.mail.re1.yahoo.com>
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On Wednesday 04 March 2009 12:34:40 pm Barney Cordoba wrote:
>
> --- On Wed, 3/4/09, John Baldwin <jhb@freebsd.org> wrote:
>
> > From: John Baldwin <jhb@freebsd.org>
> > Subject: Re: MTX Lock implementation question
> > To: freebsd-current@freebsd.org, barney_cordoba@yahoo.com
> > Cc: current@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
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