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Date: Wed, 6 Mar 2019 23:27:41 +0900 From: Sergey Senozhatsky <sergey.senozhatsky@...il.com> To: Petr Mladek <pmladek@...e.com> Cc: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>, Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Steven Rostedt <rostedt@...dmis.org>, John Ogness <john.ogness@...utronix.de>, Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, linux-kernel@...r.kernel.org Subject: Re: [RFC PATCH] printk: Introduce "store now but print later" prefix. 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
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