linux-kernel - Re: [PATCH resend] virtio_console: Free buffers from out-queue upon close

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Message-ID: <20121108085913.GA31962@amit.redhat.com>
Date:	Thu, 8 Nov 2012 09:59:13 +0100
From:	Amit Shah <amit.shah@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	sjur.brandeland@...ricsson.com,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, sjur@...ndeland.net
Subject: Re: [PATCH resend] virtio_console: Free buffers from out-queue upon
 close

On (Thu) 08 Nov 2012 [10:28:53], Rusty Russell wrote:
> sjur.brandeland@...ricsson.com writes:
> 
> > From: Sjur Brændeland <sjur.brandeland@...ricsson.com>
> >
> > Free pending output buffers from the virtio out-queue when
> > host has acknowledged port_close. Also removed WARN_ON()
> > in remove_port_data().
> >
> > Signed-off-by: Sjur Brændeland <sjur.brandeland@...ricsson.com>
> > ---
> >
> > Resending, this time including a proper "Subject"...
> > --
> >
> > Hi Amit,
> >
> > Note: This patch is compile tested only. I have done the removal
> > of buffers from out-queue in handle_control_message()
> > when host has acked the close request. This seems less
> > racy than doing it in the release function.
> 
> This confuses me... why are we doing this in case
> VIRTIO_CONSOLE_PORT_OPEN:?
> 
> We can't pull unconsumed buffers out of the ring when the other side may
> still access it, and this seems to be doing that.

Yes -- and it's my fault; I asked Sjur to do that in the close fops
function.

We should only do this in the port remove case (unplug or device
remove) -- so the original patch, with just the WARN_ON removed is the
right way.

I'll send the revised 3/3 patch for you.

		Amit
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