Re: [PATCH net v2] napi: fix race inside napi_enable

[Sukadev Bhattiprolu <sukadev@linux.ibm.com>]

Jakub Kicinski [kuba@kernel.org] wrote:
> On Mon, 18 Oct 2021 16:36:36 -0700 Dany Madden wrote:
> > > The BUG_ON() is here to make sure that when napi_enable() is called the
> > > napi instance was dormant, i.e. disabled. We have "STATE_SCHED" bit set
> > > on disabled NAPIs because that bit means ownership. Whoever disabled
> > > the NAPI owns it.
> > > 
> > > That BUG_ON() could have been taken outside of the loop, there's no
> > > point re-checking on every try.
> > > 
> > > Are you seeing NAPI-related failures? We had at least 3 reports in the
> > > last two weeks of strange failures which look like NAPI state getting
> > > corrupted on net-next...  
> > 
> > We hit two napi related crashes while attempting mtu size change.

BTW these are with a couple of bug fixes in ibmvnic driver applied
to 1e0083bd0777 ("gve: DQO: avoid unused variable warnings").

We are trying to narrow it down to the following change that is
required to be able to change mtu on ibmvnic.

> 
> Is it reproducible or happens rarely and randomly?

Random. We have been testing for a couple of weeks but hit both today.

Sukadev

---
index 8f17096e614d..a1533979c670 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -1914,8 +1914,6 @@ static netdev_tx_t ibmvnic_xmit(struct sk_buff *skb, struct net_device *netdev)
        ind_bufp = &tx_scrq->ind_buf;
 
        if (test_bit(0, &adapter->resetting)) {
-               if (!netif_subqueue_stopped(netdev, skb))
-                       netif_stop_subqueue(netdev, queue_num);
                dev_kfree_skb_any(skb);