netdev - Re: WARN_ON() in netconsole with PREEMPT

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Date:   Sat, 24 Nov 2018 20:15:45 +0100
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Eric Dumazet <edumazet@...gle.com>,
        Dave Jones <davej@...emonkey.org.uk>, netdev@...r.kernel.org,
        linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Subject: Re: WARN_ON() in netconsole with PREEMPT_RT

Hi.

On 12.11.2018 03:01, Steven Rostedt wrote:
> On Sun, 11 Nov 2018 21:16:00 +0100
> Oleksandr Natalenko <oleksandr@...alenko.name> wrote:
>> Oh, I see that write_msg() calls netpoll_send_udp() under
>> spin_lock_irqsave(), but in PREEMPT_RT this, AFAIK, does not disable
>> interrupts.
>> 
>> So, the real question here is whether the interrupts should be indeed
>> disabled. And if so, -rt should replace spin_lock_irqsave() call there
>> with what? local_irq_save()? and get rid of the warning?
>> 
> 
> Why do we care if interrupts are disabled with PREEMPT_RT here?

I don't know, if you ask me. But the check was added intentionally with 
c9fd56b34efd0, so the author had definitely something on his mind. 
Cc'ing him.

> printk() itself has a lot of issues with PREEMPT_RT that we are working
> on dealing with. Right now netconsole is actually at the end of that
> todo list.

OK, I see.

-- 
   Oleksandr Natalenko (post-factum)