On Thu, Jul 26, 2018 at 9:08 PM Sebastian Andrzej Siewior
[off-list ref] wrote:

On 2018-07-18 20:19:15 [+0530], Pintu Kumar wrote:

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Hi All,

Hi,

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I have a question about PREEMPT_RT patch for 3.10 kernel.
I am trying to port this rt patch: 0224-printk-rt-aware.patch.patch
(see the patch below), in non-rt kernel.
I could able to successfully apply this patch after replacing:
migrate_enable/disable with preempt_enable/disable.
Things were working fine so far.

Why?

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Then, I noticed that "printk" from interrupt context is not appearing
on console (minicom), if console shell is active.
However, it appears on the dmesg output.

So, I am wondering, what could be the cause of this patch for this
behavior in non-rt kernel?
Is this the expected behavior, even on PREEMPT_RT kernel?

I *think* it is but there are hardly any prints from atomic context for
anyone to notice. And the next print from non-atomic context should
flush it out.

Yes, we observed the same behavior with CONFIG_PREEMPT_RT_FULL with
beagle bone-rt kernel 4.9.
And yes, after doing : echo "1234" > /dev/kmsg the content were flushed.
So, I guess this is the expected behavior with this patch.

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Is there a way we can fix this issue on non-rt kernel?

I would guess that a wakeup to klogd would fix it.

Sorry, can you elaborate more about "wakeup to klogd".
I wanted to try it and check.

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Please help us with your suggestions.

Thanks,
Pintu

Sebastian