linux-kernel - Re: [PATCH v3 1/6] virtio_scsi: remove ACCESS_ONCE() and smp_read_barrier

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Message-ID: <20140605101127.GA8633@infradead.org>
Date:	Thu, 5 Jun 2014 03:11:27 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	hch@....de, JBottomley@...allels.com, venkateshs@...gle.com,
	Ming Lei <tom.leiming@...il.com>
Subject: Re: [PATCH v3 1/6] virtio_scsi: remove ACCESS_ONCE() and
 smp_read_barrier_depends()

On Wed, Jun 04, 2014 at 01:34:54PM +0200, Paolo Bonzini wrote:
> From: Ming Lei <tom.leiming@...il.com>
> 
> Access to tgt->req_vq is strictly serialized by spin_lock
> of tgt->tgt_lock, so the ACCESS_ONCE() isn't necessary.
> 
> smp_read_barrier_depends() in virtscsi_req_done was introduced
> to order reading req_vq and decreasing tgt->reqs, but it isn't
> needed now because req_vq is read from
> scsi->req_vqs[vq->index - VIRTIO_SCSI_VQ_BASE] instead of
> tgt->req_vq, so remove the unnecessary barrier.
> 
> Also remove related comment about the barrier.

Looks good,

Reviewed-by: Christoph Hellwig <hch@....de>
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