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

[Eric Dumazet]

On Wed, Nov 10, 2021 at 11:56 AM Alexander Lobakin
<alexandr.lobakin@xxxxxxxxx> 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.
>

...

>
> [0] https://lore.kernel.org/netdev/20211110191126.1214-1-alexandr.lobakin@xxxxxxxxx
>
> Fixes: 719c57197010 ("net: make napi_disable() symmetric with enable")
> Suggested-by: Eric Dumazet <edumazet@xxxxxxxxxx> # for-loop
> Signed-off-by: Alexander Lobakin <alexandr.lobakin@xxxxxxxxx>
> Reviewed-by: Jesse Brandeburg <jesse.brandeburg@xxxxxxxxx>
> ---

Thanks a lot !
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>