linux-kernel - Re: PowerPC: massive "scheduling while atomic" reports

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Message-Id: <201509151053.16563.jbe@pengutronix.de>
Date:	Tue, 15 Sep 2015 10:53:15 +0200
From:	Juergen Borleis <jbe@...gutronix.de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"linux-rt-users" <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: PowerPC: massive "scheduling while atomic" reports

Hi Thomas,

On Tuesday 15 September 2015 00:05:31 Thomas Gleixner wrote:
> Please CC lkml on bug reports for RT.

Okay.

> > When running the system at least every other boot this kernel spits out
> > massive "scheduling while atomic" reports.
>
> I doubt that this only happens on every other boot. This is a
> systematic failure.

That was one of the confusing things: we booted the machine and got a bunch 
off "scheduling while atomic" reports and we re-booted it and it was silent. 
That's why we thought it might be a race instead of a systematic failure.

> [...]
> If you encounter such a 'confusing' problem the next time, then look
> out for commonalities, AKA patterns. 99% of all problems can be
> decoded via patterns. And if you look at the other call chains you'll
> find more instances of those pte_*_lock() calls, which all end up in
> kmap_atomic().

Sounds easy. But we stared with two developers on the code and the bug traces 
and were lost in the code. Seems you are in a pole position due to your 
experience with the RT preempt code.

The good news: I tried your suggested change on my system and reboot it again 
and again since an hour now and no more "scheduling while atomic" reports 
occur. \o/

Thank you very much
Juergen

-- 
Pengutronix e.K.                              | Juergen Borleis             |
Industrial Linux Solutions                    | http://www.pengutronix.de/  |
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