linux-kernel - Re: console: lockup on boot

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Message-ID: <1402563262.5171.2.camel@marge.simpson.net>
Date:	Thu, 12 Jun 2014 10:54:22 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Peter Hurley <peter@...leysoftware.com>, pmladek@...e.cz,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jet Chen <jet.chen@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: console: lockup on boot

On Thu, 2014-06-12 at 10:26 +0200, Jan Kara wrote: 
> On Wed 11-06-14 23:07:04, Sasha Levin wrote:

> > The first patch fixed it (I assumed that there's no need to try the second).
>   Good. So that shows that it is the increased lockdep coverage which is
> causing problems - with my patch, lockdep is able to identify some problem
> because console drivers are now called with lockdep enabled. But because
> the problem was found in some difficult context, lockdep just hung the
> machine when trying to report it... Sadly the stacktraces you posted don't
> tell us what lockdep found.
> 
> Adding Peter Zijlstra to CC. Peter, any idea how lockdep could report
> problems when holding logbuf_lock? One possibility would be to extend
> logbuf_cpu recursion logic to every holder of logbuf_lock. That will at
> least avoid the spinlock recursion killing the machine but we won't be able
> to see what lockdep found...

Could tell lockdep to use trace_printk().

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