Received:  by oss.sgi.com id <S42211AbQFWQs3>;
	Fri, 23 Jun 2000 09:48:29 -0700
Received: from dialup326.canberra.net.au ([203.33.188.198]:1035 "HELO halfway")
	by oss.sgi.com with SMTP id <S42182AbQFWQsM>;
	Fri, 23 Jun 2000 09:48:12 -0700
Received: from linuxcare.com.au (localhost [127.0.0.1])
	by halfway (Postfix) with ESMTP
	id AA5BB8154; Sat, 24 Jun 2000 02:48:05 +1000 (EST)
From:   Rusty Russell <rusty@linuxcare.com.au>
To:     Keith Owens <kaos@ocs.com.au>,
        Philipp Rumpf <prumpf@puffin.external.hp.com>,
        Andrew Morton <andrewm@uow.edu.au>,
        Alan Cox <alan@lxorguk.ukuu.org.uk>,
        "netdev@oss.sgi.com" <netdev@oss.sgi.com>
Subject: Re: modular net drivers 
Date:   Sat, 24 Jun 2000 02:48:05 +1000
Message-Id: <20000623164805.AA5BB8154@halfway>
Sender: owner-netdev@oss.sgi.com
Precedence: bulk
Return-Path: <owner-netdev@oss.sgi.com>
X-Orcpt: rfc822;netdev-outgoing

In message <20000622174858.304CE8154@halfway> I wrote:
> OK.  Here is how it would work:

Alternate solution to avoid module problems: Phil Rumpf and I came up
with basically identical answers.  It assumes that MOD_INC_USE_COUNT
is always called in user context, and involves no changes to module
code.

1) static volatile int freeze[NR_CPUS];

2) sys_delete_module fires off a RT kernel thread for every other
   CPU:
	... /* Fire off #CPUs - 1 threads */

    retry:
	for (i = 0; i < smp_num_cpus(); i++)
		if (!freeze[i] && i != smp_processor_id())
			goto retry;

	if (atomic_read(&mod->uc.use) == 0)
		mod->cleanup();
	else
		err = -EBUSY;
	memset(freeze, 0, sizeof(freeze));

3) Threads do:
	freeze[smp_processor_id()] = 1;
	while (freeze[smp_processor_id()]);
	exit

That effectively freezes the other cpus, and cleanup() can sleep et al.
No more races.

Problems?
Rusty.
--
Hacking time.

------- End of Forwarded Message