Date: Mon, 11 Feb 2013 11:37:15 -0500
From: "J. Bruce Fields" <bfields@fieldses.org>
To: Stanislav Kinsbursky <skinsbursky@parallels.com>
Cc: akpm@linux-foundation.org, linux-nfs@vger.kernel.org,
        Trond.Myklebust@netapp.com, linux-kernel@vger.kernel.org,
        devel@openvz.org
Subject: Re: [PATCH 0/2] NFSD: fix races in service per-net resources
 allocation
Message-ID: <20130211163715.GA19342@fieldses.org>
References: <20130201111046.24066.72836.stgit@localhost.localdomain>
 <20130211002558.GD10161@fieldses.org>
 <51188D2A.4070605@parallels.com>
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In-Reply-To: <51188D2A.4070605@parallels.com>
Sender: linux-nfs-owner@vger.kernel.org

On Mon, Feb 11, 2013 at 10:18:18AM +0400, Stanislav Kinsbursky wrote:
> This one looks a bit complicated and confusing to me. Probably because
> I'm not that familiar with service transports processing logic.  So,
> as I can see, we now try to run over all per-net pool-assigned
> transports, remove them from "ready" queue and delete one by one.
> Then we try to enqueue all temporary sockets. But where in enqueueing
> of permanent sockets? I.e. how does they be destroyed with this patch?
> Then we once again try to run over all per-net pool-assigned
> transports, remove them from "ready" queue and delete one by one.  Why
> twice? I.e. why not just lose them, then enqueue them and
> svc_clean_up_xprts()?

I think you missed the first svc_close_list?:

> >  	svc_close_list(serv, &serv->sv_permsocks, net);
> >+	svc_clean_up_xprts(serv, net);
> >+	svc_close_list(serv, &serv->sv_tempsocks, net);
> >+	svc_clean_up_xprts(serv, net);

The idea is that before we'd like to close all the listeners first, so
that they aren't busy creating more tempsocks while we're trying to
close them.

I overlooked a race, though: if another thread was already handling an
accept for one of the listeners then it might not get closed by that
first svc_clean_up_xprts.

I guess we could do something like:

	delay = 0;

    again:
	numclosed = svc_close_list(serv, &serv->sv_permsocks, net);
	numclosed += svc_close_list(serv, &serv->sv_tempsocks, net);
	if (numclosed) {
		svc_clean_up_xprts(serv, net);
		msleep(delay++);
		goto again;
	}

Seems a little cheesy, but if we don't care much about shutdown
performance in a rare corner case, maybe it's the simplest way out?

--b