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

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Message-ID: <55B8D26A.7000402@hurleysoftware.com>
Date:	Wed, 29 Jul 2015 09:17:30 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Thomas Gleixner <tglx@...utronix.de>
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>
Subject: Re: [RFC PATCH v2 0/3] genirq, serial: 8250: Workaround to avoid
 irq=0 for console

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?

--- >% --
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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