Re: iounmap() - can't always unmap memory I've mappedt

From: Timur Tabi (ttabi@interactivesi.com)
Date: Fri Sep 29 2000 - 17:12:58 EST

** Reply to message from Alan Cox <alan@lxorguk.ukuu.org.uk> on Fri, 29 Sep
2000 23:00:16 +0100 (BST)

> > "num_pages" is usually just equal to 1. This code appears to work very well.
> > However, when I call the iounmap function on the memory obtained via
> > ioremap_nocache, sometimes I hit a kernel BUG(). The code which causes the bug
> > is in page_alloc.c, line 85 (in function __free_pages_ok):
> >
> > if (page->buffers)
> > BUG();
>
> This sounds like you are trying to do maps on pages that are in use. No can do

Why not? I mean, I can access the memory anyway from the driver, since it's
all mapped linearly via phys_to_virt. All I'm really doing is creating a
temporary alias.

Unfortunately, this mapping is a requirement for our product. I'd hate to have
to create my own pte's and do it all manually.

What confuses me is what ioremap_nocache() doesn't fail. Why are these tests
(e.g. page->buffers) not in ioremap_nocache()? 

-- 
Timur Tabi - ttabi@interactivesi.com
Interactive Silicon - http://www.interactivesi.com

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