linux-kernel - Re: [PATCHv7 4/4] virtio_console: Add support for remoteproc serial

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Date:	Fri, 02 Nov 2012 09:52:08 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Amit Shah <amit.shah@...hat.com>
Cc:	sjur.brandeland@...ricsson.com,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Ohad Ben-Cohen <ohad@...ery.com>, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, sjurbren@...il.com
Subject: Re: [PATCHv7 4/4] virtio_console: Add support for remoteproc serial

Amit Shah <amit.shah@...hat.com> writes:
> On (Tue) 23 Oct 2012 [12:17:49], Rusty Russell wrote:
>> sjur.brandeland@...ricsson.com writes:
>> > From: Sjur Brændeland <sjur.brandeland@...ricsson.com>
>
>> > @@ -1415,7 +1524,16 @@ static void remove_port_data(struct port *port)
>> >  
>> >  	/* Remove buffers we queued up for the Host to send us data in. */
>> >  	while ((buf = virtqueue_detach_unused_buf(port->in_vq)))
>> > -		free_buf(buf);
>> > +		free_buf(buf, true);
>> > +
>> > +	/*
>> > +	 * Remove buffers from out queue for rproc-serial. We cannot afford
>> > +	 * to leak any DMA mem, so reclaim this memory even if this might be
>> > +	 * racy for the remote processor.
>> > +	 */
>> > +	if (is_rproc_serial(port->portdev->vdev))
>> > +		while ((buf = virtqueue_detach_unused_buf(port->out_vq)))
>> > +			free_buf(buf, true);
>> >  }
>> 
>> This seems wrong; either this is needed even if !is_rproc_serial(), or
>> it's not necessary as the out_vq is empty.
>> 
>> Every path I can see has the device reset (in which case the queues
>> should not be active), or we got a VIRTIO_CONSOLE_PORT_REMOVE event (in
>> which case, the same).
>> 
>> I think we can have non-blocking writes which could leave buffers in
>> out_vq: Amit?
>
> Those get 'reclaimed' just above this hunk:
>
>
> static void remove_port_data(struct port *port)
> {
> 	struct port_buffer *buf;
>
> 	/* Remove unused data this port might have received. */
> 	discard_port_data(port);
>
> 	reclaim_consumed_buffers(port);
>
> 	/* Remove buffers we queued up for the Host to send us data in. */
> 	while ((buf = virtqueue_detach_unused_buf(port->in_vq)))
> 	      free_buf(buf, true);

No, that's pending input buffers, not output buffers.

Cheers,
Rusty.
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