linux-kernel - Re: printk considered harmful (was: [TECH TOPIC] asynchronous printk)

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Message-ID: <20161103173153.GA423@swordfish>
Date:   Fri, 4 Nov 2016 02:31:53 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Jiri Kosina <jikos@...nel.org>, Theodore Tso <tytso@....edu>,
        Hannes Reinecke <hare@...e.de>, Jan Kara <jack@...e.com>,
        Petr Mladek <pmladek@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: printk considered harmful (was: [TECH TOPIC] asynchronous printk)

[Cc linux-kernel]

Hello,

On (11/02/16 10:06), Joe Perches wrote:
> Hello all.
> 
> Can you please post notes for whatever is proposed here somewhere?

we covered 4 topics:

#1 deadlocks and recursion in printk
discussion outcome:
  I published an updated printk_safe patch last week (addresses recursion
  problems in printk). there was no strong opposition, and we agreed
  that per-cpu buffers can help us out.

discussion outcome:
  we agreed that deadlocks in printk must be addressed via printk
  indirection. basically printk() will behave the same way as
  printk_deferred() and, thus, we can, at some point, remove
  printk_deferred().

#2 async printk
discussion outcome:
  we agreed to offload printing duty to a special printk kthread.

#3 pr_cont
discussion outcome:
  out of "problems" list. no work will be done in this area.

#4 console semaphore
discussion outcome:
  we agreed that we can do better here and that it makes sense to do
  what's been proposed in my slides. but, I keep it as a low priority.
  frankly. I'd be happy to see #1-#3 in the mainline in 9-12 months.
  not because it's such an enormesoly hard thing to do, but because we
  probably would want to introduce those changes iteratively, in
  different releases.

p.s.
I uploaded "some sort" of slides to
http://www.slideshare.net/SergeySENOZHATSKY/printk-considered-harmful

	-ss