linux-kernel - Re: [PATCH] dma_declare_coherent

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Message-Id: <1177260725.4268.9.camel@mulgrave.il.steeleye.com>
Date:	Sun, 22 Apr 2007 11:52:05 -0500
From:	James Bottomley <James.Bottomley@...elEye.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma_declare_coherent_memory wrong allocation

On Fri, 2007-04-13 at 20:08 +0200, Guennadi Liakhovetski wrote:
> Either I've finally gone blind on this Friday 13th or... Looks like this 
> almost 3 year old function has a bug. Patch below compile-tested... in a 
> way.

No, it's a longstanding bug in the x86 implementation, thanks for
finding it.

> -	int bitmap_size = (pages + 31)/32;
> +	int bitmap_size = DIV_ROUND_UP(pages, 8);

This isn't quite right.  Bitmaps are arrays of longs, not arrays of
bytes.  The bug is forgetting that kmalloc() takes bytes ...

How about

int bitmap_size = DIV_ROUNDUP(pages, 32) * 4;

?

James


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