From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Runyu Xiao <runyu.xiao@seu.edu.cn>
Cc: "David S . Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Simon Horman <horms@kernel.org>,
Clark Williams <clrkwllms@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-rt-devel@lists.linux.dev, stable@vger.kernel.org,
Jianhao Xu <jianhao.xu@seu.edu.cn>
Subject: Re: [PATCH net] net: gen_estimator: protect seqcount updates from hardirq readers
Date: Wed, 23 Sep 2026 08:24:54 +0200 [thread overview]
Message-ID: <20260923062454.0W45uc5U@linutronix.de> (raw)
In-Reply-To: <20260923032936.2020902-1-runyu.xiao@seu.edu.cn>
On 2026-09-23 11:29:36 [+0800], Runyu Xiao wrote:
> est_timer updates the estimator seqcount with preemption disabled, which
> does not exclude hardirq readers on non-PREEMPT_RT kernels. A reader can
> observe an odd sequence and spin while the timer is interrupted.
How do you inject a reader from hardirq? Isn't this meant for softirq
context only?
> Disable interrupts around the seqcount write section.
>
> The failure mode was reproduced with an x86_64 kernel under QEMU. A
> test-only hardirq injection invokes gen_estimator_read() on the same CPU
> while est_timer() is updating the sequence counter.
>
> On the unfixed kernel, the hardirq reader reports the seqcount lockdep
> warning and spins until QEMU times out. With this change, the reader is
> deferred until the writer restores local IRQs, then returns and the guest
> shuts down normally. The hardirq context is deliberately injected to
> exercise this interleaving; ordinary userspace traffic does not guarantee
> it.
>
> Fixes: 1c0d32fde5bd ("net_sched: gen_estimator: complete rewrite of rate estimators")
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>
Sebastian
next prev parent reply other threads:[~2026-09-23 6:24 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-23 3:29 [PATCH net] net: gen_estimator: protect seqcount updates from hardirq readers Runyu Xiao
2026-09-23 6:24 ` Sebastian Andrzej Siewior [this message]
2026-09-23 7:43 ` Runyu Xiao
2026-09-23 7:12 ` Eric Dumazet
2026-09-24 3:29 ` sashiko-bot
2026-09-27 4:02 ` netdev-bot+sashiko
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