linux-kernel - Re: [rcf/patch] netpoll: Make it RT friendly

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Date:   Wed, 15 Dec 2021 20:54:40 +0100
From:   Mike Galbraith <efault@....de>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        RT <linux-rt-users@...r.kernel.org>
Subject: Re: [rcf/patch] netpoll: Make it RT friendly

On Wed, 2021-12-15 at 17:06 +0100, Sebastian Andrzej Siewior wrote:
>
> What is the context for netpoll_send_skb()? Why do we need to disable BH
> + RCU on RT?

Because rcu_dereference_bh() says it better be, but..

> If interrupts are never disabled, doesn't this break the assumption made
> in netpoll_tx_running()?
>
> queue_process() is also busted.

..that makes it kinda moot, and wasn't unexpected. It works, or at
least netconsole does, and lockdep was fine with it, but I figured it
unlikely to fly.  In fact, I had already taken the silence as a "Surely
you jest" or such.

	-Mike