netdev - Re: [PATCH net] net: sched: gred: prevent races when adding offloads to stats

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Message-ID: <7e0d5d6891697d24f9f9509fb8626ea9129b5eb2.camel@redhat.com>
Date:   Tue, 17 Jan 2023 10:00:56 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
        Linux Kernel Functional Testing <lkft@...aro.org>,
        jhs@...atatu.com, jiri@...nulli.us, john.hurley@...ronome.com
Subject: Re: [PATCH net] net: sched: gred: prevent races when adding
 offloads to stats

Hello,

On Sat, 2023-01-14 at 18:20 -0800, Cong Wang wrote:
> On Thu, Jan 12, 2023 at 08:41:37PM -0800, Jakub Kicinski wrote:
> > Naresh reports seeing a warning that gred is calling
> > u64_stats_update_begin() with preemption enabled.
> > Arnd points out it's coming from _bstats_update().
> 
> 
> The stack trace looks confusing to me without further decoding.
> 
> Are you sure we use sch->qstats/bstats in __dev_queue_xmit() there
> not any netdev stats? It may be a false positive one as they may end up
> with the same lockdep class.

I'm unsure I read you comment correctly. Please note that the
referenced message includes several splats. The first one - arguably
the most relevant - points to the lack of locking in the gred control
path.

The posted patch LGTM, could you please re-phrase your doubts?

Thanks,

Paolo