From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: [PATCH] virtio_net: invoke softirqs after __napi_schedule Date: Wed, 16 May 2012 10:57:13 +0300 Message-ID: <20120516075712.GA2921@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, "Michael S. Tsirkin" To: David Miller Return-path: Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: netdev.vger.kernel.org __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. Reported-by: Ulrich Obergfell Tested-by: Ulrich Obergfell Signed-off-by: Michael S. Tsirkin --- To test, one can hack try_fill_recv to always report oom. I'm not sure it's not too late for 3.4, but we can try. Rusty, could you review ASAP pls? drivers/net/virtio_net.c | 2 ++ 1 files changed, 2 insertions(+), 0 deletions(-) diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index af8acc8..cbefe67 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(); } } -- MST