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On Thu, Jun 21, 2007 at 04:02:41PM +0200, Juan RP wrote:
> On Thu, 21 Jun 2007 14:53:20 +0100
> Andrew Doran <ad@netbsd.org> wrote:
>=20
> > 1. sysmon_envsys_find()
> >=20
> > 	mutex_enter(&sme_mtx);
> > 	LIST_FOREACH(sme, &sysmon_envsys_list, sme_list) {
> > 		if (strcmp(sme->sme_name, name) =3D=3D 0)
> > 			break;
> > 	}
> > 	mutex_exit(&sme_mtx);
> > 	return sme;
> >=20
> > How do you know the item is still there after you drop sme_mtx? Can it =
be
> > taken off the list as soon as you unlock?
>=20
> I check in the parts that use sysmon_envsys_find() if returned is NULL,
> isn't it enough? or are you talking about something else?

I think the concern is that sysmon_envsys_find can find something, but=20
since you don't do reference counting, as soon as you return it as found,=
=20
another thread can remove it from the list and presumably destroy it.

The mutex does a great job of protecting the list, but nothing protects=20
the entries after you take a reference.

Take care,

Bill

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