linux-kernel - Re: Spinlock recursion in hvc

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Date:	Wed, 06 Aug 2008 10:12:46 +0100
From:	Alex Nixon <alex.nixon@...rix.com>
To:	Christian Borntraeger <borntraeger@...ibm.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: Spinlock recursion in hvc_poll

Christian Borntraeger wrote:
> Am Dienstag, 5. August 2008 schrieb Jeremy Fitzhardinge:
>> Alex Nixon wrote:
>>>>> Well I say fixed - it just means I can proceed to a spinlock recursion
>>>>> BUG() 2 secs into the boot process
> 
> Ok, this is a guess, I dont fully understand the backtrace.
> 
> request_irq tries to call the handler if the IRQ is shared. The irq handler 
> calls hvc_poll and hvc_kill which might take the same spinlock. 
> Can you test it this patch fixes the problem?

The patch appears to fix things.

- Alex

> 
> Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
> ---
>  drivers/char/hvc_console.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6/drivers/char/hvc_console.c
> ===================================================================
> --- linux-2.6.orig/drivers/char/hvc_console.c
> +++ linux-2.6/drivers/char/hvc_console.c
> @@ -322,10 +322,11 @@ static int hvc_open(struct tty_struct *t
>  
>  	hp->tty = tty;
>  
> +	spin_unlock_irqrestore(&hp->lock, flags);
> +
>  	if (hp->ops->notifier_add)
>  		rc = hp->ops->notifier_add(hp, hp->data);
>  
> -	spin_unlock_irqrestore(&hp->lock, flags);
>  
>  
>  	/*
> 

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