linux-kernel - Re: [ANNOUNCE] v5.0.3-rt1

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Message-ID: <28ab7caf-1ada-1c39-c2f9-cd69b2376ef8@arm.com>
Date:   Tue, 26 Mar 2019 10:26:31 +0000
From:   Julien Grall <julien.grall@....com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Dave P Martin <Dave.Martin@....com>
Subject: Re: [ANNOUNCE] v5.0.3-rt1

Hi John,

On 3/25/19 10:34 AM, John Ogness wrote:
> On 2019-03-25, Julien Grall <julien.grall@....com> wrote:
>> [...]
>> [    1.169151] 002: Serial: AMBA PL011 UART driver
>> [    1.254891] 002: 7ff80000.uart: ttyAMA0 at MMIO 0x7ff80000 (irq = 32, base_baud = 0) is a PL011 rev3
>> [    1.255007] 002: printk: console [ttyAMA0] enabled
> 
> The ttyAMA drivers do not have support for atomic printing, so it is not
> the new atomic feature that is causing the mangling. For your setup, all
> printk console printing is being handled within a specific context, the
> printk kernel thread.

This series is somehow making worst when using ttyAMA0. I haven't see 
any mangling with 4.19-rt.

> 
> It looks to me like some userspace application (systemd?) is writing
> directly to /dev/ttyAMA0. If the kernel is also writing to this device
> (because it is setup as a console), then the output will be
> mangled. There is no high-level synchronization between console output
> and directly writing to UART devices. Maybe you need to set your
> loglevel so that the kernel does not do the printing? For example,
> loglevel=1?

I am a bit confused with your suggestion. This would basically means I 
would not be able to see kernel warning. So this would impair any 
development on Linux-rt.

> 
> You should see this problem with older kernel versions as well.

I have tried with 4.19-rt and didn't see a similar issue. The trace 
comes pretty clean in one go. With 5.0-rt, the trace never come clean.

Cheers,

-- 
Julien Grall