Date:   Thu, 11 Nov 2021 12:50:44 -0800
From:   Sukadev Bhattiprolu <sukadev@linux.ibm.com>
To:     Alexander Lobakin <alexandr.lobakin@intel.com>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Jesse Brandeburg <jesse.brandeburg@intel.com>,
        Maciej Fijalkowski <maciej.fijalkowski@intel.com>,
        Michal Swiatkowski <michal.swiatkowski@intel.com>,
        Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
        Antoine Tenart <atenart@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        Wei Wang <weiwan@google.com>,
        =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= <bjorn@kernel.org>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 net] net: fix premature exit from NAPI state polling
 in napi_disable()
Message-ID: <YY2CJL+dQ3fgK82Y@us.ibm.com>
References: <20211110195605.1304-1-alexandr.lobakin@intel.com>
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Alexander Lobakin [alexandr.lobakin@intel.com] 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/dc6902364a8f91c4292fe1c5e01b24be@imap.linux.ibm.com/

Sukadev