Messages in this thread | | | Date | Mon, 08 Jul 2013 16:52:26 +0400 | From | Sergei Shtylyov <> | Subject | Re: [PATCH 2/2] virtio_net: fix race in RX VQ processing |
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Hello.
On 08-07-2013 13:04, Michael S. Tsirkin wrote:
> virtio net called virtqueue_enable_cq on RX path after napi_complete, so > with NAPI_STATE_SCHED clear - outside the implicit napi lock. > This violates the requirement to synchronize virtqueue_enable_cq wrt > virtqueue_add_buf. In particular, used event can move backwards, > causing us to lose interrupts. > In a debug build, this can trigger panic within START_USE.
> Jason Wang reports that he can trigger the races artificially, > by adding udelay() in virtqueue_enable_cb() after virtio_mb().
> However, we must call napi_complete to clear NAPI_STATE_SCHED before > polling the virtqueue for used buffers, otherwise napi_schedule_prep in > a callback will fail, causing us to lose RX events.
> To fix, call virtqueue_enable_cb_prepare with NAPI_STATE_SCHED > set (under napi lock), later call virtqueue_poll with > NAPI_STATE_SCHED clear (outside the lock).
> Reported-by: Jason Wang <jasowang@redhat.com> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com> > --- > drivers/net/virtio_net.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-)
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index 5305bd1..fbdd79a 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -622,8 +622,9 @@ again: > > /* Out of packets? */ > if (received < budget) { > + unsigned r = virtqueue_enable_cb_prepare(rq->vq);
Empty line wouldn't hurt here, after declaration.
WBR, Sergei
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