linux-kernel - Re: [RFC][PATCHv6 00/12] printk: introduce printing kernel thread

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Date:   Thu, 14 Dec 2017 12:55:06 -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>,
        Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [RFC][PATCHv6 00/12] printk: introduce printing kernel thread

On Thu, 14 Dec 2017 07:25:51 -0800
Tejun Heo <tj@...nel.org> wrote:

> > 3. Soft-lockups are still theoretically possible with Steven's
> >    approach.
> > 
> >    But it seems to be quite efficient in many real life scenarios,
> >    including Tetsuo's stress testing. Or am I wrong?  
> 
> AFAICS, Steven's approach doesn't fix the livelock that we see quite
> often in the fleet where we don't have a safe context to keep flushing
> messages.  This isn't theoretical at all.  You simply don't have a
> safe context on the cpu to go to.  I said I'd come back with a repro
> case but haven't had a chance to yet.  I'll try to do it before the
> end of the year, but idk this is pretty obvious.

Yes! Please create a reproducer, because I still don't believe there is
one. And it's all hand waving until there's an actual report that we can
lock up the system with my approach.

-- Steve