linux-kernel - Re: [PATCH 1/1] omap: Ptr "isr_reg" tracked as NULL was dereferenced

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Date:	Wed, 06 Oct 2010 10:33:22 +0400
From:	Evgeny Kuznetsov <EXT-Eugeny.Kuznetsov@...ia.com>
To:	ext Kevin Hilman <khilman@...prootsystems.com>, balbi@...com
Cc:	balbi@...com, "tony@...mide.com" <tony@...mide.com>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"zmc@...ian.net" <zmc@...ian.net>,
	"a.j.buxton@...il.com" <a.j.buxton@...il.com>
Subject: Re: [PATCH 1/1] omap: Ptr "isr_reg" tracked as NULL was
 dereferenced

On Tue, 2010-10-05 at 08:01 -0700, ext Kevin Hilman wrote:
> Felipe Balbi <balbi@...com> writes:
> 
> > Hi,
> >
> > On Tue, Oct 05, 2010 at 03:42:10AM -0500, Evgeny Kuznetsov wrote:
> >>+	if (!isr_reg) {
> >>+		printk(KERN_ERR "FATAL: Incorrect GPIO method %i\n",
> >>+				bank->method);
> >>+		BUG();
> >>+		}
> >
> > this could be simply:
> >
> > BUG_ON(!isr_reg);
> 
> WARN_ON is better.
> 
> A BUG() will panic the kernel and stop everything.  This is not an error
> condition that should prevent the entire kernel from running.

'isr_reg' is dereferenced later in code:
	...
	isr_saved = isr = __raw_readl(isr_reg) & enabled;
	...
So this will stop kernel anyway.
I just hoped to help in understanding of issue by log line. WARN_ON
could be used for this.

As a variant compilation error could be added, to prevent situation when
kernel is incorrectly configured.
E.g.:
#if !defined(CONFIG_ARCH_OMAP1) &&		
	!defined(CONFIG_ARCH_OMAP15XX) &&	
	!defined(CONFIG_ARCH_OMAP16XX) &&	
	!defined(CONFIG_ARCH_OMAP730) &&	
	!defined(CONFIG_ARCH_OMAP850) &&	
	!defined(CONFIG_ARCH_OMAP2) &&	
	!defined(CONFIG_ARCH_OMAP3) &&	
	!defined(CONFIG_ARCH_OMAP4)

#error "Incorrect arch configuration"
#endif

But there are still cases when 'isr_reg' could have NULL value (if
'bank->method' is not equal to configured one).

Regards,
Evgeny
> 
> From asm-generic/bug.h:
> 
> /*
>  * Don't use BUG() or BUG_ON() unless there's really no way out; one
>  * example might be detecting data structure corruption in the middle
>  * of an operation that can't be backed out of.  If the (sub)system
>  * can somehow continue operating, perhaps with reduced functionality,
>  * it's probably not BUG-worthy.
>  *
>  * If you're tempted to BUG(), think again:  is completely giving up
>  * really the *only* solution?  There are usually better options, where
>  * users don't need to reboot ASAP and can mostly shut down cleanly.
>  */



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