Message-ID: <1490858435.4696.25.camel@gmx.de>
Subject: Re: Random guest crashes since 5c34d002dcc7 ("virtio_pci: use
 shared interrupts for virtqueues")
From: Mike Galbraith <efault@gmx.de>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>,
        Thorsten Leemhuis <linux@leemhuis.info>,
        virtio-dev@lists.oasis-open.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        rjones@redhat.com
Date: Thu, 30 Mar 2017 09:20:35 +0200
In-Reply-To: <1490843414.4167.11.camel@gmx.de>
References: <f49abfcc-723e-fa91-bda0-198f4a0da0c0@leemhuis.info>
         <20170323145622.GA31690@lst.de> <1490605644.14634.50.camel@gmx.de>
         <20170327170540.GA28715@lst.de> <1490638711.26533.44.camel@gmx.de>
         <1490768602.5950.25.camel@gmx.de>
         <20170329230936-mutt-send-email-mst@kernel.org>
         <1490843414.4167.11.camel@gmx.de>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1526
Lines: 39

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);