linux-kernel - Re: [PATCH] MAINTAINERS: Add printk maintainers

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Message-ID: <20161215172336.GA3124@twins.programming.kicks-ass.net>
Date:   Thu, 15 Dec 2016 18:23:36 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Petr Mladek <pmladek@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MAINTAINERS: Add printk maintainers

On Thu, Dec 15, 2016 at 12:20:27PM -0500, Steven Rostedt wrote:
> On Thu, 15 Dec 2016 18:12:00 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Thu, Dec 15, 2016 at 03:34:43PM +0100, Petr Mladek wrote:
> > > We have to find the right balance. For example, we do not show
> > > messages immediately in NMI context because there is a risk
> > > of a deadlock.  
> > 
> > I find the occasional deadlock much preferable to guaranteed no output.
> 
> Right, we can't stress the importance of getting output out when it
> happens. A printk dump is the first course of action when debugging a
> crash. And the printk output shows how much progress the computer made.
> 
> If all printks are asynchronous, that will be unreliable information.

No, that will be _no_ information, since the 'later' part that does the
flush will never happen.

> And really, that information can be extremely useful, but only if it is
> reliable, otherwise, it becomes useless.

Well, if you want reliable get a UART and those 3 patches I did to force
early_printk :-)