linux-kernel - Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup

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Date:   Wed, 10 Jan 2018 13:45:04 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        Cong Wang <xiyou.wangcong@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        rostedt@...e.goodmis.org, Byungchul Park <byungchul.park@....com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup

On Wed, 10 Jan 2018 10:14:59 -0800
Tejun Heo <tj@...nel.org> wrote:

> On Wed, Jan 10, 2018 at 10:12:52AM -0800, Tejun Heo wrote:
> > Hello, Steven.
> > 
> > So, everything else on your message, sure.  You do what you have to
> > do, but I really don't understand the following part, and this has
> > been the main source of frustration in the whole discussion.
> > 
> > On Wed, Jan 10, 2018 at 01:05:17PM -0500, Steven Rostedt wrote:  
> > > You on the other hand are showing unrealistic scenarios, and crying
> > > that it's what you see in production, with no proof of it.  
> > 
> > I've explained the same scenario multiple times.  Unless you're
> > assuming that I'm lying, it should be amply clear that the scenario is
> > unrealistic - we've been seeing them taking place repeatedly for quite
> > a while.  
> 
> Oops, I meant to write "not unrealistic".  Anyways, if you think I'm
> lying, please let me know.  I can ask others who have been seeing the
> issue to join the thread.

I don't believe you are lying. I believe you are interpreting one
problem as another. I don't see this is a printk bug, I see it as a
recursive OOM + net console bug. My patch is not trying to solve that,
and I don't believe it should be solved via printk.

I'm trying to solve the problem of printk spamming all CPUs causing a
single CPU to lock up. That is a real bug that has been hit in various
different scenarios, where there is no other underlying bug. This issue
is a printk problem, and my solution solves it for printk.

-- Steve