linux-kernel - Re: [PATCH 1/3] net/bridge/br_if.c: don't use _WORK

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Message-ID: <20070219145613.GB75@tv-sign.ru>
Date:	Mon, 19 Feb 2007 17:56:13 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	David Howells <dhowells@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jarek Poplawski <jarkao2@...pl>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] net/bridge/br_if.c: don't use _WORK_NAR

On 02/19, David Howells wrote:
>
> Hmmm...  You've got a work_struct (well, a delayed_work actually) - can you
> just punt the destruction of the object over to keventd to perform, I wonder?

Yes, this is close (I think) to what I suggested, see below,

> The big problem with that that I see is that the workqueue facility has no
> guards in place against a work_struct's handler function running on several
> CPUs at once in response to the same work_struct.

Yes. And for this problem WORK_STRUCT_NOAUTOREL does help, but not so much.
It can prevent re-scheduling of the same work, but only if work->func() did
not do work_release() yet.

> > I think the fix should be so that port_carrier_check() does get/put on
> > "struct net_bridge_port" (container), but not on "struct net_device", and
> 
> I'm not sure how this helps.  You still have to get rid of the net_device at
> some point.

Yes, destroy_nbp() does dev_put(dev). del_nbp() sets dev->br_port = NULL,
port_carrier_check() goes to "done" in that case. So everething looks safe
to me (but again, I do not even know what the "bridge" is :), so we should
only take care about container, nothing more.

I'll try to make a patch for illustration on evening.

Oleg.

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