From: Rusty Russell <redacted>
Date: Thu, 17 May 2012 13:02:53 +0930

On Wed, 16 May 2012 10:57:13 +0300, "Michael S. Tsirkin" [off-list ref] wrote:

quoted

__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 <redacted>
Tested-by: Ulrich Obergfell <redacted>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

 ...

Acked-by: Rusty Russell <redacted>

Michael, you're best to submit this directly to Linus as I just
made what I hope is my last push to him for 3.4 today.