[PATCH net-next v4 0/2] virtio-net: don't busy poll for cvq command

[Jason Wang <jasowang@redhat.com>]

Hi all:

The code used to busy poll for cvq command which turns out to have
several side effects:

1) infinite poll for buggy devices
2) bad interaction with scheduler

So this series tries to use cond_resched() in the waiting loop. Before
doing this we need first make sure the cvq command is not executed in
atomic environment, so we need first convert rx mode handling to a
workqueue.

Note that, this doesn't try to solve the case that a malicous device
may block networking stack (RTNL) or break freezer which requries more
thought to gracefully exit and resend the commands.

Please review.

Changes since V3:

- Tweak the comments
- Tweak the changelog to explain the rx mode lost after resuming.
- No functional changes

Changes since V2:

- Don't use interrupt but cond_resched()

Changes since V1:

- use RTNL to synchronize rx mode worker
- use completion for simplicity
- don't try to harden CVQ command

Changes since RFC:

- switch to use BAD_RING in virtio_break_device()
- check virtqueue_is_broken() after being woken up
- use more_used() instead of virtqueue_get_buf() to allow caller to
  get buffers afterwards
- break the virtio-net device when timeout
- get buffer manually since the virtio core check more_used() instead

Jason Wang (2):
  virtio-net: convert rx mode setting to use workqueue
  virtio-net: add cond_resched() to the command waiting loop

 drivers/net/virtio_net.c | 59 +++++++++++++++++++++++++++++++++++++---
 1 file changed, 55 insertions(+), 4 deletions(-)

-- 
2.39.3