Subject: Re: [PATCH v2 net] net: fix premature exit from NAPI state polling in napi_disable()

From: Sukadev Bhattiprolu <[email-masked]>
Date: Thu, 11 Nov 2021 12:50:44 -0800

Alexander Lobakin [[email-masked]] wrote:
> Commit 719c57197010 ("net: make napi_disable() symmetric with
> enable") accidentally introduced a bug sometimes leading to a kernel
> BUG when bringing an iface up/down under heavy traffic load.
> 
> Prior to this commit, napi_disable() was polling n->state until
> none of (NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC) is set and then
> always flip them. Now there's a possibility to get away with the
> NAPIF_STATE_SCHE unset as 'continue' drops us to the cmpxchg()
> call with an unitialized variable, rather than straight to
> another round of the state check.

Thanks. Tested v1 and it fixes the problem discussed at:

https://lore.kernel.org/netdev/[email-masked]/

Sukadev