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From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	John Ogness <john.ogness@linutronix.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] printk: Introduce "store now but print later" prefix.
Date: Wed, 6 Mar 2019 23:27:41 +0900	[thread overview]
Message-ID: <20190306142741.GA21163@tigerII.localdomain> (raw)
In-Reply-To: <20190306100404.jzfk7oqsh3turqth@pathway.suse.cz>

On (03/06/19 11:04), Petr Mladek wrote:
> > I'm suggesting to use a non-async printk() for $trailer_text_line line. I think
> > that changing all printk() called from out_of_memory() to async is doable, if
> > the caller of out_of_memory() wakes up a dedicated kthread described below.
> 
> This is error prone. The trailing printk is not guaranteed:
> 
>     + It might get lost by code refactoring.
> 
>     + People would miss that it is needed when async printk is used
>       in a shared function, e.g. dump_stack().
> 
>     + People will not know that it is needed because they
>       are not familiar with the API. The would just use it
>       as part of a cargo cult programming or so.
> 
> For this reason, this API is a "no no no" from my side.

Conceptually, this buffering is just pr_cont() with extension
from "1 line" to "N lines". pr_cont() also waits for a special
marker to flush the buffered data - that marker is pr_cont('\n'),
which forces printk to log_store() cont buffer. In Tetsuo's
proposal the marker is different. That's the only difference I
see. Should any other CPU printk() anything - it will print out
buffered data, same thing as pr_cont(), again.

	-ss

  reply	other threads:[~2019-03-06 14:27 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-23  4:42 [RFC PATCH] printk: Introduce "store now but print later" prefix Tetsuo Handa
2019-03-04  3:22 ` Sergey Senozhatsky
2019-03-04 11:40   ` Tetsuo Handa
2019-03-04 12:09     ` Sergey Senozhatsky
2019-03-04 14:23     ` Petr Mladek
2019-03-04 14:37       ` Sergey Senozhatsky
2019-03-05  1:23       ` Tetsuo Handa
2019-03-05  7:52         ` Sergey Senozhatsky
2019-03-05 12:57         ` Michal Hocko
2019-03-06 10:04         ` Petr Mladek
2019-03-06 14:27           ` Sergey Senozhatsky [this message]
2019-03-06 18:24           ` Tetsuo Handa
2019-03-15 10:49             ` Tetsuo Handa
2019-03-20 15:04             ` Petr Mladek
2019-03-20 15:25             ` ratelimit API: was: " Petr Mladek
2019-03-21  8:13               ` Tetsuo Handa
2019-03-21  8:49                 ` Michal Hocko

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