linux-kernel - Re: [PATCH v3 2/3] hvc_init(): Enforce one-time initialization.

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Message-ID: <20111216060048.GA12211@amit-x200.redhat.com>
Date:	Fri, 16 Dec 2011 11:30:48 +0530
From:	Amit Shah <amit.shah@...hat.com>
To:	Miche Baker-Harvey <miche@...gle.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	xen-devel@...ts.xensource.com,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Anton Blanchard <anton@...ba.org>,
	Mike Waychison <mikew@...gle.com>,
	ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
	Eric Northrup <digitaleric@...gle.com>
Subject: Re: [PATCH v3 2/3] hvc_init(): Enforce one-time initialization.

On (Tue) 06 Dec 2011 [09:05:38], Miche Baker-Harvey wrote:
> Amit,
> 
> Ah, indeed.  I am not using MSI-X, so virtio_pci::vp_try_to_find_vqs()
> calls vp_request_intx() and sets up an interrupt callback.  From
> there, when an interrupt occurs, the stack looks something like this:
> 
> virtio_pci::vp_interrupt()
>   virtio_pci::vp_vring_interrupt()
>     virtio_ring::vring_interrupt()
>       vq->vq.callback()  <-- in this case, that's virtio_console::control_intr()
>         workqueue::schedule_work()
>           workqueue::queue_work()
>             queue_work_on(get_cpu())  <-- queues the work on the current CPU.
> 
> I'm not doing anything to keep multiple control message from being
> sent concurrently to the guest, and we will take those interrupts on
> any CPU. I've confirmed that the two instances of
> handle_control_message() are occurring on different CPUs.

Hi Miche,

Here's a quick-and-dirty hack that should help.  I've not tested this,
and it's not yet signed-off-by.  Let me know if this helps.

>From 16708fa247c0dd34aa55d78166d65e463f9be6d6 Mon Sep 17 00:00:00 2001
Message-Id: <16708fa247c0dd34aa55d78166d65e463f9be6d6.1324015123.git.amit.shah@...hat.com>
From: Amit Shah <amit.shah@...hat.com>
Date: Fri, 16 Dec 2011 11:27:04 +0530
Subject: [PATCH 1/1] virtio: console: Serialise control work

We currently allow multiple instances of the control work handler to run
in parallel.  This isn't expected to work; serialise access by disabling
interrupts on new packets from the Host and enable them when all the
existing ones are consumed.
---
 drivers/char/virtio_console.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 8e3c46d..72d396c 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -1466,6 +1466,7 @@ static void control_work_handler(struct work_struct *work)
 	portdev = container_of(work, struct ports_device, control_work);
 	vq = portdev->c_ivq;
 
+ start:
 	spin_lock(&portdev->cvq_lock);
 	while ((buf = virtqueue_get_buf(vq, &len))) {
 		spin_unlock(&portdev->cvq_lock);
@@ -1483,6 +1484,10 @@ static void control_work_handler(struct work_struct *work)
 		}
 	}
 	spin_unlock(&portdev->cvq_lock);
+	if (unlikely(!virtqueue_enable_cb(vq))) {
+		virtqueue_disable_cb(vq);
+		goto start;
+	}
 }
 
 static void out_intr(struct virtqueue *vq)
@@ -1533,6 +1538,7 @@ static void control_intr(struct virtqueue *vq)
 {
 	struct ports_device *portdev;
 
+	virtqueue_disable_cb(vq);
 	portdev = vq->vdev->priv;
 	schedule_work(&portdev->control_work);
 }
-- 
1.7.7.4



		Amit
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