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

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Date:	Fri, 2 Nov 2012 15:50:47 +0530
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>,
	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

On (Fri) 02 Nov 2012 [09:52:08], Rusty Russell wrote:
> 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.

You're right.  Nice catch.

Sjur, can you remove the WARN_ON in your latest series, even generic
ports may have buffers in the outq.

It'll also need to be done in the port_fops_release() function.  Let
me know if you prefer I send a patch instead.

Thanks,
		Amit
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