Date: Wed, 28 Aug 2002 12:31:48 -0700 From: Mike Makonnen <makonnen@pacbell.net> To: smp@FreeBSD.ORG Subject: Locking questions Message-ID: <20020828123148.7717f871.makonnen@pacbell.net>
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Hi folks,
I resumed working on my resource limit lock patch, and I have a couple of
questions.
1. I get "duplicate lock of same type" witness warnings because of this:
limhold(plimit) { lock(plimit), bump refcount, unlock(plimit) }
newlim = limget();
PROC_LOCK(p2);
PROC_LOCK(p1);
LIM_LOCK(p1->p_limit);
if (p1->p_limit->p_lflags & PL_SHAREMOD) {
limcopy(newlim, p1->p_limit);
p2->p_limit = limhold(newlim);
} else {
p2->p_limit = limhold(p1->p_limit);
}
LIM_UNLOCK(p1->p_limit);
PROC_UNLOCK(p1);
PROC_UNLOCK(p2);
limfree(newlim);
newlim = NULL;
I get this message in limhold() because of:
p2->p_limit = limhold(p1->p_limit);
Why is this bad?
Is it safe to drop the p1->p_plimit lock
right before I do the hold? It should be because you need
both a PROC_LOCK and a LIM_LOCK to modify the plimit.
2. Should I add the plimit lock to
static struct witness_order_list_entry order_lists[] ?
What is the rationale behind the ordering of the list?
Cheers,
Mike Makonnen
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