From: Jakub Kicinski <kuba@kernel.org>
To: Paolo Abeni <pabeni@redhat.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>,
davem@davemloft.net, netdev@vger.kernel.org, edumazet@google.com,
Linux Kernel Functional Testing <lkft@linaro.org>,
jhs@mojatatu.com, jiri@resnulli.us, john.hurley@netronome.com
Subject: Re: [PATCH net] net: sched: gred: prevent races when adding offloads to stats
Date: Tue, 17 Jan 2023 11:10:19 -0800 [thread overview]
Message-ID: <20230117111019.50c47ea1@kernel.org> (raw)
In-Reply-To: <7e0d5d6891697d24f9f9509fb8626ea9129b5eb2.camel@redhat.com>
On Tue, 17 Jan 2023 10:00:56 +0100 Paolo Abeni wrote:
> 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 didn't repro this myself, TBH, but there is u64_stats_update_begin()
inside _bstats_update(). Pretty sure it will trigger the warning that
preemption is not disabled on non-SMP systems.
> 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.
Yup, I'm not really sure if we're fixing the right splat for the bug.
But I am fairly confident we should be holding a lock while writing
bstats from the dump path, enqueue/dequeue may run concurrently.
> The posted patch LGTM, could you please re-phrase your doubts?
next prev parent reply other threads:[~2023-01-17 20:17 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-13 4:41 [PATCH net] net: sched: gred: prevent races when adding offloads to stats Jakub Kicinski
2023-01-15 2:20 ` Cong Wang
2023-01-17 9:00 ` Paolo Abeni
2023-01-17 19:10 ` Jakub Kicinski [this message]
2023-01-19 20:19 ` Cong Wang
2023-01-19 21:16 ` Jakub Kicinski
2023-01-19 20:17 ` Cong Wang
2023-01-19 5:10 ` patchwork-bot+netdevbpf
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