Re: [ANNOUNCE] v5.0.3-rt1

[Julien Grall]

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,
> 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