virtio_net: use non-reentrant workqueue.

Michael S. Tsirkin also noticed that we could run the refill work
multiple CPUs: if we kick off a refill on one CPU and then on another,
they would both manipulate the queue at the same time (they use
napi_disable to avoid racing against the receive handler itself).

Tejun points out that this is what the WQ_NON_REENTRANT flag is for,
and that there is a convenient system kthread we can use.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 07ca150..2055386 100644 (file)
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -508,7 +508,7 @@ static void refill_work(struct work_struct *work)
        /* In theory, this can happen: if we don't get any buffers in
         * we will *never* try to fill again. */
        if (still_empty)
-               schedule_delayed_work(&vi->refill, HZ/2);
+               queue_delayed_work(system_nrt_wq, &vi->refill, HZ/2);
 }
 
 static int virtnet_poll(struct napi_struct *napi, int budget)
@@ -527,7 +527,7 @@ again:
 
        if (vi->num < vi->max / 2) {
                if (!try_fill_recv(vi, GFP_ATOMIC))
-                       schedule_delayed_work(&vi->refill, 0);
+                       queue_delayed_work(system_nrt_wq, &vi->refill, 0);
        }
 
        /* Out of packets? */
@@ -729,7 +729,7 @@ static int virtnet_open(struct net_device *dev)
 
        /* Make sure we have some buffers: if oom use wq. */
        if (!try_fill_recv(vi, GFP_KERNEL))
-               schedule_delayed_work(&vi->refill, 0);
+               queue_delayed_work(system_nrt_wq, &vi->refill, 0);
 
        virtnet_napi_enable(vi);
        return 0;