linux-kernel - Re: [PATCH v4 0/4] Cleaning printk stuff in NMI context

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Message-ID: <20160121113007.GC3305@pathway.suse.cz>
Date:	Thu, 21 Jan 2016 12:30:07 +0100
From:	Petr Mladek <pmladek@...e.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Arnd Bergmann <arnd@...db.de>, jkosina@...e.com,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Daniel Thompson <daniel.thompson@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v4 0/4] Cleaning printk stuff in NMI context

On Wed 2016-01-20 13:17:13, Andrew Morton wrote:
> On Fri, 11 Dec 2015 14:20:48 +0100 Petr Mladek <pmladek@...e.com> wrote:
> 
> > this is just a quick respin of the previous version. It changes
> > the few details as you suggested. Also it fixes the build problem
> > on ARM as reported by Geert and Arnd.
> > 
> > I rather send the whole patch set because there is the renamed header.
> > Also the extra blank space affects two patches. I hope that it will
> > safe you some work. Please, let me know if you would prefer
> > incremental patches.
> > 
> > 
> > Changes against v3:
> > 
> >   + used size_t for "len" and "size"
> > 
> >   + replaced WARN() with pr_err()
> > 
> >   + renamed kernel/printk/printk.h -> internal.h
> > 
> >   + fixed build on ARM (undefined NMI_LOG_BUF_SHIFT)
> 
> So the review of the v3 patchset was ...  inconclusive.  And everyone has
> gone quiet about v4.
>
> Probably because you didn't cc the V3 discussion participants when
> sending out V4.  Big mistake, sorry, I can't check everything!

Ah, v4 was sent too fast after v3 before others reacted. It included
rather cosmetic changes based on your (Andrew's) feedback.


> But v4 is basically unaltered from v3 so can we please rev this up
> again?  yay or nay?  Thanks.

The patch set prevents deadlocks that happen in a real life. It
increases a chance to get a valid crash dump when NMI is involved.

It does not handle well the situation when NMI is involved and
the crash dump could not get produced. But this is not handled
well even now. As Peter Zijlstra writes this a usually a real
mess when he needs to use special hacks (early_printk) anyway.

I still believe that the patch set makes sense and is acceptable
as is.

Thanks for taking care of it,
Petr