From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1756756AbcJWUdq (ORCPT <rfc822;w@1wt.eu>);
        Sun, 23 Oct 2016 16:33:46 -0400
Received: from smtprelay0225.hostedemail.com ([216.40.44.225]:53122 "EHLO
        smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL)
        by vger.kernel.org with ESMTP id S1756705AbcJWUdp (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Sun, 23 Oct 2016 16:33:45 -0400
X-Session-Marker: 6A6F6540706572636865732E636F6D
X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,joe@perches.com,:::::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1373:1437:1515:1516:1518:1534:1541:1593:1594:1711:1730:1747:1777:1792:2194:2199:2393:2553:2559:2562:2693:2828:3138:3139:3140:3141:3142:3353:3622:3865:3866:3867:3868:3870:3871:3872:3873:3874:4321:4470:5007:6119:6691:7875:7903:8792:9040:9108:10004:10400:10848:11232:11658:11914:12663:12740:12760:13069:13161:13229:13311:13357:13439:14096:14097:14181:14659:14721:14777:21080:21433:30054:30060:30090:30091,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0,LFtime:1,LUA_SUMMARY:none
X-HE-Tag: house62_77aba89362a18
X-Filterd-Recvd-Size: 2996
Message-ID: <1477254821.3561.8.camel@perches.com>
Subject: Re: linux.git: printk() problem
From: Joe Perches <joe@perches.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Petr Mladek <pmladek@suse.cz>
Date: Sun, 23 Oct 2016 13:33:41 -0700
In-Reply-To: <CA+55aFwOBR6z55r2abAT_TuYTHfyuc8f75B2+Z7+Lhr9fzSZRA@mail.gmail.com>
References: <201610122230.DID43237.FSOHFFQOJOtVML@I-love.SAKURA.ne.jp>
         <CA+55aFwLLxVKZcN4qm0GH0sHk70xRE8e4s8_ma6WYafao85Rfw@mail.gmail.com>
         <CAMuHMdXUqOhv37mTvX+ic45VsgvM1g3=McWAa1WCeVYH+KohCw@mail.gmail.com>
         <CA+55aFw1Z95Lfefr1PfZW17qj9zjv+-bZ-oPESTNk+tbAEVrhQ@mail.gmail.com>
         <1477249607.3561.2.camel@perches.com>
         <CA+55aFwOBR6z55r2abAT_TuYTHfyuc8f75B2+Z7+Lhr9fzSZRA@mail.gmail.com>
Content-Type: text/plain; charset="ISO-8859-1"
X-Mailer: Evolution 3.22.0-2ubuntu1 
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Sun, 2016-10-23 at 12:32 -0700, Linus Torvalds wrote:
> On Sun, Oct 23, 2016 at 12:06 PM, Joe Perches <joe@perches.com> wrote:
> > On Sun, 2016-10-23 at 11:11 -0700, Linus Torvalds wrote:
> > > 
> > > And those two per se sound fairly easy to handle ("KERN_CONT means
> > > append to the line buffer, otherwise flush the line buffer and move to
> > > the record buffer").
> > > 
> > > But what complicates things more is then the "console output", which
> > > has two issues:
> > > 
> > >  - it is done outside the locking regime for the line buffer and the
> > > record buffer.
> > > 
> > >  - it is done on _partial_ line buffers.
> > 
> > 
> > EOL KERN_<LEVEL> and thread interleaving still exists.
> 
> 
> Note that the thread interleaving is still trivial: it's easily done
> at the point where we decide "can we append to the line buffer or
> not". That's pretty simple. Just flush the record when the thread
> changes.
> 
> So the interleaving will never go away, it's very fundamental - unless
> we make the line buffer just be a per-thread thing. And yes, that
> would be the cleanest solution, but it's also an extra buffer for each
> thread, so realistically it's just not going to happen.

I doubt there are cases where more than a few of
these interleaving threads are simultaneous.

Perhaps it could be a pool of active thread
continuation buffers.  

> End result: I'm not worried about the interleaving. It will cause ugly
> output, but we've always had that, and the solution to it is "if you
> absolutely don't want interleaving, then don't try to print partial
> lines!".
> The classic "don't do that then" response, in other world.

Yup, best solution.