linux-kernel - RE: [PATCH v5 1/2] PRUSS UIO driver support

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Date:	Mon, 28 Feb 2011 09:32:54 +0530
From:	"TK, Pratheesh Gangadhar" <pratheesh@...com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"davinci-linux-open-source@...ux.davincidsp.com" 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	"hjk@...sjkoch.de" <hjk@...sjkoch.de>,
	"gregkh@...e.de" <gregkh@...e.de>,
	"sshtylyov@...sta.com" <sshtylyov@...sta.com>,
	"arnd@...db.de" <arnd@...db.de>,
	"Chatterjee, Amit" <amit.chatterjee@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH v5 1/2] PRUSS UIO driver support

Hi,

> -----Original Message-----
> From: Thomas Gleixner [mailto:tglx@...utronix.de]
> Sent: Friday, February 25, 2011 3:24 PM
> To: TK, Pratheesh Gangadhar
> Cc: davinci-linux-open-source@...ux.davincidsp.com; hjk@...sjkoch.de;
> gregkh@...e.de; sshtylyov@...sta.com; arnd@...db.de; Chatterjee, Amit;
> linux-kernel@...r.kernel.org; linux-arm-kernel@...ts.infradead.org
> Subject: Re: [PATCH v5 1/2] PRUSS UIO driver support
> 
> On Fri, 25 Feb 2011, Pratheesh Gangadhar wrote:
> > +static irqreturn_t pruss_handler(int irq, struct uio_info *dev_info)
> > +{
> > +	void __iomem *base = dev_info->mem[0].internal_addr;
> > +	void __iomem *intren_reg = base + PINTC_HIER;
> > +	void __iomem *intrstat_reg = base + PINTC_HIPIR + ((irq - 1) << 2);
> > +	int val = ioread32(intren_reg), intr_mask = (1 << (irq - 1));
> > +
> > +	/* Is interrupt enabled and active ? */
> > +	if (!(val & intr_mask) && (ioread32(intrstat_reg) & HIPIR_NOPEND))
> > +		return IRQ_NONE;
> > +
> > +	/* Disable interrupt */
> > +	iowrite32((val & ~intr_mask), intren_reg);
> > +	return IRQ_HANDLED;
> > +}
> 
> Hmm, just noticed, that you fiddle with the interrupt enable register
> here totally unprotected. So on a SMP system you might haandle two
> different interrupts at the same time. That wants locking.
> 
> And even on UP, you have a problem as you reenable that thing from
> user space which requires a read modify write. Racy as hell.
> 
> Please look at the other UIO drivers which have the same problem.
> Sorry for not noticing earlier!

Thanks for pointing this out. Yes - this is a problem especially since we have more than one interrupt for PRUSS which is enabled/disabled in this register. I will fix this and resubmit along with fixes addressing Sergei's comments on platform specific portion.

Thanks,
Pratheesh

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