From ec13ee80145ccb95b00e6e610044bbd94a170051 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Wed, 16 May 2012 10:57:12 +0300 Subject: [PATCH] virtio_net: invoke softirqs after __napi_schedule __napi_schedule might raise softirq but nothing causes do_softirq to trigger, so it does not in fact run. As a result, the error message "NOHZ: local_softirq_pending 08" sometimes occurs during boot of a KVM guest when the network service is started and we are oom: ... Bringing up loopback interface: [ OK ] Bringing up interface eth0: Determining IP information for eth0...NOHZ: local_softirq_pending 08 done. [ OK ] ... Further, receive queue processing might get delayed indefinitely until some interrupt triggers: virtio_net expected napi to be run immediately. One way to cause do_softirq to be executed is by invoking local_bh_enable(). As __napi_schedule is normally called from bh or irq context, this seems to make sense: disable bh before __napi_schedule and enable afterwards. In fact it's a very complicated way of calling do_softirq(), and works since this function is only used when we are not in interrupt context. It's not hot at all, in any ideal scenario. Reported-by: Ulrich Obergfell Tested-by: Ulrich Obergfell Signed-off-by: Michael S. Tsirkin Acked-by: Rusty Russell --- drivers/net/virtio_net.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index af8acc85f4bb..cbefe671bcc6 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -492,7 +492,9 @@ static void virtnet_napi_enable(struct virtnet_info *vi) * We synchronize against interrupts via NAPI_STATE_SCHED */ if (napi_schedule_prep(&vi->napi)) { virtqueue_disable_cb(vi->rvq); + local_bh_disable(); __napi_schedule(&vi->napi); + local_bh_enable(); } } -- 2.30.2