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Date: Thu, 24 Jul 2008 08:53:29 +0200
To: Ingo Molnar <mingo@elte.hu>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, linux-kernel@vger.kernel.org,
       Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [lockdep warning] INFO: inconsistent lock state,
	serial8250_interrupt(), &port_lock_key
Message-ID: <20080724065329.GE17724@gollum.tnic>
Reply-To: petkovbb@gmail.com
Mail-Followup-To: petkovbb@gmail.com, Ingo Molnar <mingo@elte.hu>,
	Alan Cox <alan@lxorguk.ukuu.org.uk>, linux-kernel@vger.kernel.org,
	Peter Zijlstra <a.p.zijlstra@chello.nl>
References: <20080723093332.GA22109@elte.hu> <20080723093604.GA29817@elte.hu>
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User-Agent: Mutt/1.5.17+20080114 (2008-01-14)
From: Borislav Petkov <petkovbb@googlemail.com>
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On Wed, Jul 23, 2008 at 11:36:04AM +0200, Ingo Molnar wrote:
> 
> * Ingo Molnar <mingo@elte.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.

Signed-off-by: Borislav Petkov <petkovbb@gmail.com>

--
diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 27f34a9..55eca08 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -1874,7 +1874,7 @@ static int serial8250_startup(struct uart_port *port)
 		 * the interrupt is enabled.  Delays are necessary to
 		 * allow register changes to become visible.
 		 */
-		spin_lock(&up->port.lock);
+		spin_lock_irqsave(&up->port.lock, flags);
 		if (up->port.flags & UPF_SHARE_IRQ)
 			disable_irq_nosync(up->port.irq);
 
@@ -1890,7 +1890,7 @@ static int serial8250_startup(struct uart_port *port)
 
 		if (up->port.flags & UPF_SHARE_IRQ)
 			enable_irq(up->port.irq);
-		spin_unlock(&up->port.lock);
+		spin_unlock_irqrestore(&up->port.lock, flags);
 
 		/*
 		 * If the interrupt is not reasserted, setup a timer to

-- 
Regards/Gruß,
    Boris.