linux-kernel - Re: [RFC][PATCH v6 0/2] printk: Make printk() completely async

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Date:	Sun, 24 Apr 2016 15:35:22 +0200
From:	Pavel Machek <pavel@....cz>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Jan Kara <jack@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.com>, Petr Mladek <pmladek@...e.com>,
	Tejun Heo <tj@...nel.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	linux-kernel@...r.kernel.org,
	Byungchul Park <byungchul.park@....com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [RFC][PATCH v6 0/2] printk: Make printk() completely async

On Sun 2016-04-24 14:14:49, Sergey Senozhatsky wrote:
> On (04/23/16 21:40), Pavel Machek wrote:
> [..]
> > > > The patch set is against next-20160321
> > > > 
> > > > the series in total has 3 patches:
> > > > - printk: Make printk() completely async
> > > > - printk: Make wake_up_klogd_work_func() async
> > > > - printk: make console_unlock() async
> > > > 
> > > > per discussion, "printk: make console_unlock() async" will be posted
> > > > later on.
> > > 
> > > Patches look good to me. I don't think you need to mention the
> > > console_unlock() async patch when it is not part of the series.  BTW, you
> > > seemed to have dropped my patch to skip if there are too many buffered
> > > messages when oops is in progress. Any reason for that?
> > 
> > So... from basically linux 0.0, cli() printk("") could be used for
> > debugging. ... and that's now gone. Right?
> > 
> > Can you explain why that is good idea?
> 
> it's not gone. you need to explicitly enable async printk mode. the case
> you mentioned -- cli() printk("")->console_unlock() -- apart from being
> useful in some scenarios, can cause problems in others, simply because
> under some circumstances it can run forever, as long as there are printk()
> calls coming from other CPUs (which can happen during, f.e., debugging).
> did you mean UP systems? well, async printk is sort of useless on UP systems
> anyway.

Well, yes, it has been long known that printk() can take long
time.. Still that's not a problem for smaller system.

Now, patch set above says "Make printk() completely async" -- so I
assumed that it does...

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html