linux-kernel - Re: Random guest crashes since 5c34d002dcc7 ("virtio_pci: use shared interrupts for virtqueues")

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Date:   Thu, 30 Mar 2017 09:20:35 +0200
From:   Mike Galbraith <efault@....de>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Christoph Hellwig <hch@....de>,
        Thorsten Leemhuis <linux@...mhuis.info>,
        virtio-dev@...ts.oasis-open.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        rjones@...hat.com
Subject: Re: Random guest crashes since 5c34d002dcc7 ("virtio_pci: use
 shared interrupts for virtqueues")

On Thu, 2017-03-30 at 05:10 +0200, Mike Galbraith wrote:

> WRT spin, you should need do nothing more than boot with threadirqs,
> that's 100% repeatable here in absolutely virgin source.

No idea why virtqueue_get_buf() in __send_control_msg() fails forever
with threadirqs, but marking that vq as being busted (it clearly is)
results in one gripe, and a vbox that seemingly cares not one whit that
something went missing.  CONFIG_DEBUG_SHIRQ OTOH notices, mutters
something that sounds like "idiot" when I hibernate the thing ;-)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index e9b7e0b3cabe..831406dae1cb 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -567,6 +567,7 @@ static ssize_t __send_control_msg(struct ports_device *portdev, u32 port_id,
 	struct scatterlist sg[1];
 	struct virtqueue *vq;
 	unsigned int len;
+	unsigned long deadline = jiffies+1;
 
 	if (!use_multiport(portdev))
 		return 0;
@@ -583,9 +584,13 @@ static ssize_t __send_control_msg(struct ports_device *portdev, u32 port_id,
 
 	if (virtqueue_add_outbuf(vq, sg, 1, &portdev->cpkt, GFP_ATOMIC) == 0) {
 		virtqueue_kick(vq);
-		while (!virtqueue_get_buf(vq, &len)
-			&& !virtqueue_is_broken(vq))
+		while (!virtqueue_get_buf(vq, &len) && !virtqueue_is_broken(vq)) {
 			cpu_relax();
+			if (time_after(jiffies, deadline)) {
+				trace_printk("Aw crap, I'm stuck.. breaking device\n");
+				virtio_break_device(portdev->vdev);
+			}
+		}
 	}
 
 	spin_unlock(&portdev->c_ovq_lock);