From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <owner-linux-mm@kvack.org>
Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197])
	by kanga.kvack.org (Postfix) with ESMTP id 866FF6B0005
	for <linux-mm@kvack.org>; Mon, 23 Apr 2018 01:35:37 -0400 (EDT)
Received: by mail-pf0-f197.google.com with SMTP id z22so5210396pfi.7
        for <linux-mm@kvack.org>; Sun, 22 Apr 2018 22:35:37 -0700 (PDT)
Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65])
        by mx.google.com with SMTPS id y5sor2432470pgp.291.2018.04.22.22.35.36
        for <linux-mm@kvack.org>
        (Google Transport Security);
        Sun, 22 Apr 2018 22:35:36 -0700 (PDT)
Date: Mon, 23 Apr 2018 14:35:31 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup
Message-ID: <20180423053531.GB3643@jagdpanzerIV>
References: <20180117134201.0a9cbbbf@gandalf.local.home>
 <20180119132052.02b89626@gandalf.local.home>
 <20180120071402.GB8371@jagdpanzerIV>
 <20180120104931.1942483e@gandalf.local.home>
 <20180121141521.GA429@tigerII.localdomain>
 <20180123064023.GA492@jagdpanzerIV>
 <20180123095652.5e14da85@gandalf.local.home>
 <20180123152130.GB429@tigerII.localdomain>
 <20180123104121.2ef96d81@gandalf.local.home>
 <20180123154347.GE1771050@devbig577.frc2.facebook.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20180123154347.GE1771050@devbig577.frc2.facebook.com>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Tejun Heo <tj@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, Petr Mladek <pmladek@suse.com>, akpm@linux-foundation.org, linux-mm@kvack.org, Cong Wang <xiyou.wangcong@gmail.com>, Dave Hansen <dave.hansen@intel.com>, Johannes Weiner <hannes@cmpxchg.org>, Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>, Vlastimil Babka <vbabka@suse.cz>, Peter Zijlstra <peterz@infradead.org>, Linus Torvalds <torvalds@linux-foundation.org>, Jan Kara <jack@suse.cz>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, rostedt@home.goodmis.org, Byungchul Park <byungchul.park@lge.com>, Pavel Machek <pavel@ucw.cz>, linux-kernel@vger.kernel.org

On (01/23/18 07:43), Tejun Heo wrote:
> > 
> > We can have more. But if printk is causing printks, that's a major bug.
> > And work queues are not going to fix it, it will just spread out the
> > pain. Have it be 100 printks, it needs to be fixed if it is happening.
> > And having all printks just generate more printks is not helpful. Even
> > if we slow them down. They will still never end.
> 
> So, at least in the case that we were seeing, it isn't that black and
> white.  printk keeps causing printks but only because printk buffer
> flushing is preventing the printk'ing context from making forward
> progress.  The key problem there is that a flushing context may get
> pinned flushing indefinitely and using a separate context does solve
> the problem.

Hello Tejun,

I'm willing to take a look at those printk()-s from console drivers.
Any chance you can send me some of the backtraces you see [the most
common/disturbing]?

	-ss