linux-kernel - Re: [PATCH] printk: Don't discard earlier unprinted messages to make space

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Date:	Thu, 22 Oct 2015 14:23:34 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	David Howells <dhowells@...hat.com>, Petr Mladek <pmladek@...e.com>
Cc:	linux-kernel@...r.kernel.org, jack@...e.cz, will.deacon@....com,
	rostedt@...dmis.org, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] printk: Don't discard earlier unprinted messages to
 make space

On Thu, 2015-10-22 at 14:19 +0100, David Howells wrote:
> Petr Mladek <pmladek@...e.com> wrote:
> 
> > I would expect that the first few messages are printed to the console
> > before the buffer is wrapped. IMHO, in many cases, you are interested
> > into the final messages that describe why the system went down.
> 
> The last message might tell you that the machine panicked because the NMI
> handler triggered due to a spinlocked section taking too long or something.
> This doesn't help if the oops that caused the spinlock to remain held or
> whatever gets discarded from the buffer due to several intervening complaints
> that result secondarily from the initial oops.
> 
> > If there is no time to print them, you want to have them in the crash dump
> > (ring buffer) at least.
> 
> But not at the expense of discarding the first oops report.  *That* one is the
> most important.
> 
> Perhaps things could be arranged such that messages *can* be discarded from
> the front of the buffer *provided* they are not oops messages.

Of course, all this is a symptom of the fact that printk is now lossy.
If you had an option to make it reliable again, you wouldn't need to
argue over *which* messages to lose.

-- 
dwmw2


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