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

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Message-Id: <20230720083839.481487-1-jasowang@redhat.com>
Date:   Thu, 20 Jul 2023 04:38:37 -0400
From:   Jason Wang <jasowang@...hat.com>
To:     mst@...hat.com, jasowang@...hat.com, xuanzhuo@...ux.alibaba.com
Cc:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        alvaro.karsz@...id-run.com, maxime.coquelin@...hat.com
Subject: [PATCH net-next v4 0/2] virtio-net: don't busy poll for cvq command

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