linux-kernel - Re: [lockdep warning] INFO: inconsistent lock state, serial8250_interrupt(), &port_lock

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Message-ID: <20080724094154.GA20128@elte.hu>
Date:	Thu, 24 Jul 2008 11:41:54 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	petkovbb@...il.com, Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [lockdep warning] INFO: inconsistent lock state,
	serial8250_interrupt(), &port_lock_key


* Borislav Petkov <petkovbb@...glemail.com> wrote:

> On Thu, Jul 24, 2008 at 08:53:29AM +0200, Borislav Petkov wrote:
> > On Wed, Jul 23, 2008 at 11:36:04AM +0200, Ingo Molnar wrote:
> > > 
> > > * Ingo Molnar <mingo@...e.hu> wrote:
> > > 
> > > > =================================
> > > > [ INFO: inconsistent lock state ]
> > > > 2.6.26-tip-06509-gb4ebc67-dirty #13600
> > > > ---------------------------------
> > > 
> > > the upstream component of that is: v2.6.26-6077-gc010b2f
> > > 
> > > i.e. my suspicion is that this got introduced via the recent tty 
> > > changes.
> > 
> > Hi,
> > 
> > i hit the same warning here. How about the following fix (this is at least what
> > i think happens):
> > --
> > 
> > serial8250_startup() might unconditionally enable irqs after releasing
> > &up->port.lock while we're still servicing an interrupt.
> 
> Actually, this explanation is not correct - it should be more like:
> 
> serial8250_startup() doesn't disable interrupts while taking the 
> &up->port.lock which might race against the interrupt handler 
> serial8250_interrupt(), which when entered, will deadlock waiting for 
> the lock to be released.

thanks Borislav, your patch seems to have done the trick.

Tested-by: Ingo Molnar <mingo@...e.hu>

	Ingo
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