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SubjectRe: Random guest crashes since 5c34d002dcc7 ("virtio_pci: use shared interrupts for virtqueues")
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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);
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