netdev - Re: [PATCH net v2] napi: fix race inside napi

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Date:   Mon, 18 Oct 2021 16:47:23 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Dany Madden <drt@...ux.ibm.com>
Cc:     Sukadev Bhattiprolu <sukadev@...ux.ibm.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, netdev@...r.kernel.org,
        linyunsheng@...wei.com, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Antoine Tenart <atenart@...nel.org>,
        Alexander Lobakin <alobakin@...me>,
        Wei Wang <weiwan@...gle.com>, Taehee Yoo <ap420073@...il.com>,
        Björn Töpel <bjorn@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Neil Horman <nhorman@...hat.com>,
        Dust Li <dust.li@...ux.alibaba.com>
Subject: Re: [PATCH net v2] napi: fix race inside napi_enable

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.

Is it reproducible or happens rarely and randomly?