[PATCH] virtio_net: use non-reentrant workqueue.

[Rusty Russell <rusty@rustcorp.com.au>]

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>
---
 drivers/net/virtio_net.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -507,7 +507,7 @@ static void refill_work(struct work_stru
 	/* 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)
@@ -526,7 +526,7 @@ 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? */
@@ -727,7 +727,7 @@ static int virtnet_open(struct net_devic
 
 	/* 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;