netdev - Re: [PATCH RFC] virtio_net: fix refill related races

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Message-ID: <20111220190946.GD10752@google.com>
Date:	Tue, 20 Dec 2011 11:09:46 -0800
From:	Tejun Heo <tj@...nel.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Amit Shah <amit.shah@...hat.com>,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] virtio_net: fix refill related races

Hello, Michael.

On Tue, Dec 20, 2011 at 09:09:08PM +0200, Michael S. Tsirkin wrote:
> Another question, wanted to make sure:
> virtnet_poll does schedule_delayed_work(&vi->refill, 0);
> separately refill work itself also does
> schedule_delayed_work(&vi->refill, HZ/2);
> If two such events happen twice, on different CPUs, we are still guaranteed
> the work will only run once, right?

No, it's not.  Normal workqueues only guarantee non-reentrance on
local CPU.  If you want to guarantee that only one instance of a given
item is executing across all CPUs, you need to use the nrt workqueue.

Thanks.

-- 
tejun
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