linux-kernel - Re: [PATCH 2/3 v2] i2c: i801: enable irq for i801 smbus transactions

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Message-ID: <20120620105847.65cf37f2@endymion.delvare>
Date:	Wed, 20 Jun 2012 10:58:47 +0200
From:	Jean Delvare <khali@...ux-fr.org>
To:	Daniel Kurtz <djkurtz@...omium.org>
Cc:	ben-linux@...ff.org, seth.heasley@...el.com, ben@...adent.org.uk,
	David.Woodhouse@...el.com, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, olofj@...omium.org,
	bleung@...omium.org
Subject: Re: [PATCH 2/3 v2] i2c: i801: enable irq for i801 smbus 
 transactions

On Tue, 19 Jun 2012 20:47:04 +0200, Jean Delvare wrote:
> On Fri,  6 Jan 2012 18:58:21 +0800, Daniel Kurtz wrote:
> > @@ -879,8 +953,24 @@ static int __devinit i801_probe(struct pci_dev *dev,
> >  	i801_probe_optional_slaves(priv);
> >  
> >  	pci_set_drvdata(dev, priv);
> > +
> > +	if (priv->features & FEATURE_IRQ) {
> > +		init_waitqueue_head(&priv->waitq);
> > +		spin_lock_init(&priv->lock);
> > +
> > +		err = request_irq(dev->irq, i801_isr, IRQF_SHARED,
> > +				  i801_driver.name, priv);
> > +		if (err) {
> > +			dev_err(&dev->dev, "Failed to allocate irq %d: %d",
> 
> Missing "\n".
> 
> > +				dev->irq, err);
> > +			goto exit_del_adapter;
> > +		}
> 
> I believe order is wrong, and interrupt handler should be installed
> _before_ registering the adapter. Otherwise you have a race condition
> where the handler could be called before the waitqueue and spinlock are
> initialized.

Oh, and it's not a theoretical thing. I can reproducibly crash the
kernel by removing and loading the i2c-i801 driver again. Swapping
request_irq() and i2c_add_adapter() solves it.

-- 
Jean Delvare
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