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

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Date:   Mon, 18 Dec 2017 12:46:13 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Tejun Heo <tj@...nel.org>,
        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
Subject: Re: [RFC][PATCHv6 00/12] printk: introduce printing kernel thread

On Mon, 18 Dec 2017 15:13:53 +0100
Petr Mladek <pmladek@...e.com> wrote:

> One question is if we really want to rely on offloading in
> this case. What if this is printed to debug some stalled
> system.

Correct, and this is what I call when debugging hard lockups, and I do
it from NMI. Which the new NMI code prevents all the data I want to
print to come out to console.

I had to create a really huge buffer to print it.

show_state_filter() is not a normal printk() call. It is used for
debugging. Not a very good example of issues that happen on production
systems. If anything, this should be disabled on a production system.

Let's just add my patch (I'll respin it if it needs it), and send it
off into the wild. Let's see if there's still reports of issues, and
then come back to solutions. Because, really, I'm still not convinced
that there's anything out there that needs much more "fixing" of
printk().

-- Steve