[PATCH RFC v2 0/4] virtio net: spurious interrupt related fixes

[Michael S. Tsirkin]

With the implementation of napi-tx in virtio driver, we clean tx
descriptors from rx napi handler, for the purpose of reducing tx
complete interrupts. But this introduces a race where tx complete
interrupt has been raised, but the handler finds there is no work to do
because we have done the work in the previous rx interrupt handler.
A similar issue exists with polling from start_xmit, it is however
less common because of the delayed cb optimization of the split ring -
but will likely affect the packed ring once that is more common.

In particular, this was reported to lead to the following warning msg:
[ 3588.010778] irq 38: nobody cared (try booting with the
"irqpoll" option)
[ 3588.017938] CPU: 4 PID: 0 Comm: swapper/4 Not tainted
5.3.0-19-generic #20~18.04.2-Ubuntu
[ 3588.017940] Call Trace:
[ 3588.017942]  <IRQ>
[ 3588.017951]  dump_stack+0x63/0x85
[ 3588.017953]  __report_bad_irq+0x35/0xc0
[ 3588.017955]  note_interrupt+0x24b/0x2a0
[ 3588.017956]  handle_irq_event_percpu+0x54/0x80
[ 3588.017957]  handle_irq_event+0x3b/0x60
[ 3588.017958]  handle_edge_irq+0x83/0x1a0
[ 3588.017961]  handle_irq+0x20/0x30
[ 3588.017964]  do_IRQ+0x50/0xe0
[ 3588.017966]  common_interrupt+0xf/0xf
[ 3588.017966]  </IRQ>
[ 3588.017989] handlers:
[ 3588.020374] [<000000001b9f1da8>] vring_interrupt
[ 3588.025099] Disabling IRQ #38

This patchset attempts to fix this by cleaning up a bunch of races
related to the handling of sq callbacks (aka tx interrupts).
Very lightly tested, sending out for help with testing, early feedback
and flames. Thanks!

Michael S. Tsirkin (4):
  virtio: fix up virtio_disable_cb
  virtio_net: disable cb aggressively
  virtio_net: move tx vq operation under tx queue lock
  virtio_net: move txq wakeups under tx q lock

 drivers/net/virtio_net.c     | 35 +++++++++++++++++++++++++++++------
 drivers/virtio/virtio_ring.c | 26 +++++++++++++++++++++++++-
 2 files changed, 54 insertions(+), 7 deletions(-)

-- 
MST