linux-kernel - Re: [RFC PATCH v2 0/3] genirq, serial: 8250: Workaround to avoid irq=0 for console

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Date:	Wed, 29 Jul 2015 15:35:42 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Peter Hurley <peter@...leysoftware.com>
cc:	Taichi Kageyama <t-kageyama@...jp.nec.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"jiang.liu@...ux.intel.com" <jiang.liu@...ux.intel.com>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jslaby@...e.cz" <jslaby@...e.cz>,
	"prarit@...hat.com" <prarit@...hat.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH v2 0/3] genirq, serial: 8250: Workaround to avoid
 irq=0 for console

On Wed, 29 Jul 2015, Peter Hurley wrote:
> On 07/29/2015 07:53 AM, Thomas Gleixner wrote:
> > On Wed, 29 Jul 2015, Peter Hurley wrote:
> >> On 07/29/2015 06:32 AM, Thomas Gleixner wrote:
> >>> On Wed, 29 Jul 2015, Taichi Kageyama wrote:
> >>>> - Keep interrupt disabled on the CPU which is used to detect 
> >>>>   an interrupt during the timeout of autoconfig_irq().
> >>>>      + Kick printk() on the CPU which detects interrupt 
> >>>>        from a console serial port.
> >>>
> >>> This is wrong to begin with. How is that supposed to work on an UP
> >>> machine? Not at all.
> >>>
> >>> So no, fix the code which has interrupts disabled accross autoprobing
> >>> and do not try to apply bandaids somewhere else.
> >>
> >> Like printk() from some unrelated driver?
> > 
> > If that's the cause for the wreckage then yes, we need a way to tell
> > the printk code not to call into the driver until that initialization
> > step is done. It's that simple.
> 
> Like this?

Looks about right.
 
> --- >% --
> Subject: [PATCH] genirq: Disable printk() during irq probe
> 
> printk() disables interrupts for extended periods of time while
> outputting to console drivers. This breaks irq probing since the
> triggered irq may not be serviced (in time) if scheduled on the
> printk() cpu.
> 
> Claim the console_lock() which effectively disables console output.
> 
> Signed-off-by: Peter Hurley <peter@...leysoftware.com>
> ---
>  kernel/irq/autoprobe.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/kernel/irq/autoprobe.c b/kernel/irq/autoprobe.c
> index 0119b9d..47535d2 100644
> --- a/kernel/irq/autoprobe.c
> +++ b/kernel/irq/autoprobe.c
> @@ -39,6 +39,13 @@ unsigned long probe_irq_on(void)
>  	 */
>  	async_synchronize_full();
>  	mutex_lock(&probing_active);
> +
> +	/*
> +	 * printk() breaks irq probing - disable printk output until probe
> +	 * completes
> +	 */
> +	console_lock();
> +
>  	/*
>  	 * something may have generated an irq long ago and we want to
>  	 * flush such a longstanding irq before considering it as spurious.
> @@ -132,6 +139,7 @@ unsigned int probe_irq_mask(unsigned long val)
>  		}
>  		raw_spin_unlock_irq(&desc->lock);
>  	}
> +	console_unlock();
>  	mutex_unlock(&probing_active);
>  
>  	return mask & val;
> @@ -174,6 +182,7 @@ int probe_irq_off(unsigned long val)
>  		}
>  		raw_spin_unlock_irq(&desc->lock);
>  	}
> +	console_unlock();
>  	mutex_unlock(&probing_active);
>  
>  	if (nr_of_irqs > 1)
> -- 
> 2.5.0
> 
> 
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