Re: [ANNOUNCE] v5.0.3-rt1

From: Julien Grall
Date: Tue Mar 26 2019 - 06:26:38 EST

Hi John,

On 3/25/19 10:34 AM, John Ogness wrote:
On 2019-03-25, Julien Grall <julien.grall@xxxxxxx> 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,

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.


Julien Grall