Date: Wed, 4 Mar 2009 10:45:43 -0800 (PST) From: Barney Cordoba <barney_cordoba@yahoo.com> To: John Baldwin <jhb@freebsd.org> Cc: current@freebsd.org Subject: Re: MTX Lock implementation question Message-ID: <440962.16587.qm@web63902.mail.re1.yahoo.com> In-Reply-To: <200903041305.54726.jhb@freebsd.org>
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--- On Wed, 3/4/09, John Baldwin <jhb@freebsd.org> wrote:
> From: John Baldwin <jhb@freebsd.org>
> Subject: Re: MTX Lock implementation question
> To: barney_cordoba@yahoo.com
> Cc: current@freebsd.org
> Date: Wednesday, March 4, 2009, 1:05 PM
> 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);
There seems to be an issue when the type is set to NULL. I got
panics in strcpy and strlen functions when displaying warning
traces that cleared up when the type was set to a string.
BC
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