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

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Message-ID: <20111214235412.GA29835@google.com>
Date:	Wed, 14 Dec 2011 15:54:12 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	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, Rusty.

On Tue, Dec 13, 2011 at 01:05:11PM +1030, Rusty Russell wrote:
> Both places where we call:
> 
> 	cancel_delayed_work_sync(&vi->refill);
> 
> Do not actually guarantee that vi->refill isn't running, because it
> can requeue itself.  A 'bool no_more_refill' field seems like the
> simplest fix for this, but I don't think it's sufficient.
> 
> Tejun, is this correct?  What's the correct way to synchronously stop a
> delayed_work which can "schedule_delayed_work(&vi->refill, HZ/2);" on
> itself?

cancel_delayed_work_sync() itself should be good enough.  It first
steals the pending state and then waits for it to finish if in-flight.
Queueing itself afterwards becomes noop.

Thanks.

-- 
tejun
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