netdev - Re: 6.12-rc1: Lockdep regression bissected (virtio-net/console/scheduler)

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Message-ID: <20241003-unbiased-adventurous-chupacabra-6c8acd@leitao>
Date: Thu, 3 Oct 2024 08:06:23 -0700
From: Breno Leitao <leitao@...ian.org>
To: peterz@...radead.org, gregkh@...uxfoundation.org, pmladek@...e.com,
	mst@...hat.com, jasowang@...hat.com, xuanzhuo@...ux.alibaba.com,
	kuba@...nel.org
Cc: virtualization@...ts.linux.dev, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, vschneid@...hat.com, axboe@...nel.dk
Subject: Re: 6.12-rc1: Lockdep regression bissected
 (virtio-net/console/scheduler)

On Thu, Oct 03, 2024 at 07:51:20AM -0700, Breno Leitao wrote:
> Upstream kernel (6.12-rc1) has a new lockdep splat, that I am sharing to
> get more visibility:
> 
> 	WARNING: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected
> 
> This is happening because the HARDIRQ-irq-unsafe "_xmit_ETHER#2" lock is
> acquired in virtnet_poll_tx() while holding the HARDIRQ-irq-safe, and
> lockdep doesn't like it much.
> 
> I've bisected the problem, and weirdly enough, this problem started to
> show up after a unrelated(?) change in the scheduler:
> 
> 	52e11f6df293e816a ("sched/fair: Implement delayed dequeue")

Errata. The commit is missing the first number. The right one is:

	152e11f6df293e816a ("sched/fair: Implement delayed dequeue")