On Friday 04 April 2008 01:46:21 pm Balaji Rao wrote:
> Hi Rusty,
>
> I hit a bug in virtio_ring.c:218 when I was stressing virtio_net using kvm with -smp 4.
>
> static void vring_disable_cb(struct virtqueue *_vq)
> {
> struct vring_virtqueue *vq = to_vvq(_vq);
>
> START_USE(vq);
> --> BUG_ON(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT);
> vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
> END_USE(vq);
> }
>
> Going through the source code, I felt that this BUG_ON is not required as any CPU could race and call disable_cb when one
> cpu still believes that its enabled. To validate my understanding, I commented out the BUG_ON and everything worked
> perfectly well.
>
> I also get a lot of "Unlikely: restart svq race" on my console. Under high load conditions, a race could occur very often
> and I'm not sure if that signals a buggy situation. We could printk_ratelimit if at all we need to retain it.
>
> If you agree, I'll send a patch to this.
>
Christian Borntraeger CCed.
BTW, this is with respect to kvm.git, not a version prior to
commit 4265f161b6bb7b31163671329b1142b9023bf4e3
Author: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Date: Fri Mar 14 14:17:05 2008 +0100
virtio: fix race in enable_cb
The above commit does not fix the problem.I see this oops even today. There is a race happening between calls to enable_cb
and disable_cb.
--
regards,
Balaji Rao
Dept. of Mechanical Engineering,
National Institute of Technology Karnataka, India
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