Date: Fri, 02 May 1997 14:00:39 +0200 From: Poul-Henning Kamp <phk@dk.tfs.com> To: Peter Dufault <dufault@hda.com> Cc: phk@dk.tfs.com (Poul-Henning Kamp), current@freebsd.org Subject: Re: vnode->v_usage Message-ID: <220.862574439@critter> In-Reply-To: Your message of "Fri, 02 May 1997 07:24:54 EDT." <199705021124.HAA27754@hda.hda.com>
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In message <199705021124.HAA27754@hda.hda.com>, Peter Dufault writes:
>The first unlock won't work since a second thread can come in and
>decide to do the same move. Obviously you have a lock ordering issue
>with the nested lock and you have to define the ordering.
see below for my solution.
>Moving items between two lists should be atomic - it is common
>and lends itself to clean implementation.
It's actually the same list in this case...
>Aside: how about making the queues truly opaque while you're doing this?
>Then you have a single place to enable locking hierarchy violation detection,
>*CAS types of implementations, etc.
I don't think that would be very easy. On the other hand, there
are very few pieces of code manipulating the vnode free list, do
it's hardly worth the effort. Or did I misunderstand you ?
Poul-Henning
void
vtouch(vp)
struct vnode *vp;
{
simple_lock(&vp->v_interlock);
if (vp->v_usecount) {
simple_unlock(&vp->v_interlock);
return;
}
if (simple_lock_try(&vnode_free_list_slock)) {
TAILQ_REMOVE(&vnode_free_list, vp, v_freelist);
TAILQ_INSERT_TAIL(&vnode_free_list, vp, v_freelist);
simple_unlock(&vnode_free_list_slock);
}
simple_unlock(&vp->v_interlock);
}
--
Poul-Henning Kamp | phk@FreeBSD.ORG FreeBSD Core-team.
http://www.freebsd.org/~phk | phk@login.dknet.dk Private mailbox.
whois: [PHK] | phk@tfs.com TRW Financial Systems, Inc.
Power and ignorance is a disgusting cocktail.
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