From mboxrd@z Thu Jan  1 00:00:00 1970
From: Rabin Vincent <rabin@rab.in>
Subject: Re: Exception while  handling MEM Hole on OMAP3 / ARM Cortex A8
Date: Tue, 18 Aug 2009 08:31:49 +0530
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To: "Aguirre Rodriguez, Sergio Alberto" <saaguirre@ti.com>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>, "Syed Mohammed, Khasim" <khasim@ti.com>, "linux-arm-kernel@lists.arm.linux.org.uk" <linux-arm-kernel@lists.arm.linux.org.uk>, "linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>

On Mon, Aug 17, 2009 at 03:23:18PM -0500, Aguirre Rodriguez, Sergio Alberto wrote:
> #ifndef CONFIG_SPARSEMEM
> int pfn_valid(unsigned long pfn)
> {
> 	struct meminfo *mi = &meminfo;
> 	unsigned int left = 0, right = mi->nr_banks;
> 
> 	while (left <= right) {

This condition will cause the while to loop forever when left == right
and pfn < bank_pfn_start(bank).

> 		unsigned int mid = (right - left) / 2;

This calculation is incorrect when left != 0 (also in the original
patch).

> 		struct membank *bank = &mi->bank[mid];
> 
> 		if (pfn < bank_pfn_start(bank))
> 			right = mid;
> 		else if (pfn >= bank_pfn_end(bank))
> 			left = mid + 1;
> 		else
> 			return 1;
> 	}
> 	return 0;
> }
> EXPORT_SYMBOL(pfn_valid);
> #endif

Here's a fixed version:

int pfn_valid(unsigned long pfn)
{
	struct meminfo *mi = &meminfo;
	unsigned int left = 0, right = mi->nr_banks;

	while (left < right) {
			unsigned int mid = (left + right) / 2;
			struct membank *bank = &mi->bank[mid];

			if (pfn < bank_pfn_start(bank))
				right = mid;
			else if (pfn >= bank_pfn_end(bank))
				left = mid + 1;
			else
				return 1;
	}

	return 0;
}

Rabin