linux-kernel - Re: [PATCH RFC] virtio-balloon: fix add/get API use

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Message-ID: <87ipe4w6hf.fsf@rustcorp.com.au>
Date:	Wed, 04 Jul 2012 12:57:40 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Rafael Aquini <aquini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	virtualization <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH RFC] virtio-balloon: fix add/get API use

On Mon, 2 Jul 2012 10:33:08 +0300, "Michael S. Tsirkin" <mst@...hat.com> wrote:
> In virtio balloon virtqueue_get_buf might now run concurrently with
> virtqueue_kick.  I audited both and this seems safe in practice but
> this is not guaranteed by the API.
> Additionally, a spurious interrupt might in theory make
> virtqueue_get_buf run in parallel with virtqueue_add_buf, which is racy.
> 
> While we might try to protect against spurious callbacks it's
> easier to fix the driver: balloon seems to be the only one
> (mis)using the API like this, so let's just fix balloon.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>

I was thinking of a spinlock, but this is far more elegant.

And I added an explicit reference to the 'virtio: expose added
descriptors immediately.' commit in your commit msg.

Kudos!
Rusty.
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