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Date:   Fri, 22 Mar 2019 18:52:48 +0000
From:   Julien Grall <>
To:     Sebastian Andrzej Siewior <>,
        Thomas Gleixner <>
Cc:     LKML <>,
        linux-rt-users <>,
        Steven Rostedt <>,, Dave P Martin <>
Subject: Re: [ANNOUNCE] v5.0.3-rt1


Apologies for a possible stupid question.

On 20/03/2019 17:15, Sebastian Andrzej Siewior wrote:
>    - Applied John Ogness' prinkt rework. One visible change is the
>      output during boot. Under the hood and for RT: By default, output
>      that is created at KERN_WARN[0] or higher is printed immediately if the
>      console supports "atomic" print (currently the 8250 driver does).
>      This output is printed immediately (and visible) even from IRQ-off
>      or preempt-disabled regions which wasn't the case earlier. This will
>      raise the latency at run-time *but* there should be no WARNING,
>      ERROR or PANIC messages at run-time on a fully working system.
>      Messages with lower severity are printed "later" by a kthread.

Using 5.0.3-rt1, I get some warning message completely mangled with the rest of 
the output (e.g systemd message) but also between them. Some excerpt of a 500 
lines lockdep warning (AFAICT the printk is not related to the printk code):

[   52.294547] 005: ... which became HARDIRQ-irq-unsafe at:
[   52.294553] 005: ...
[   52.294554] 005:   lock_acquire+0xf8/0x318
[  OK  ] Reached target
t_spin_lock+0x48/0x70  lock_acquire+0xf8/0x318
[0;1;39mRemote File Systems.[   52.294570] 005:   iommu_dma_map_msi_msg+0x5c/0x1

[   52.296824] 005: CPU: 5 PID: 2108 Comm: ip Not tainted 5.0.3-rt1-00007-g42ede
9a0fed6 #4312] 005:  __sys_sendmsg+0x68/0xb8

I understand the new series add support for "atomic" print. So I am wondering 
whether this issue is related to it? Is there any advice to prevent the mangling?


Julien Grall

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