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

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

[Alan Cox]

> "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

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

[Timur Tabi]

** 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()?


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

[Alan Cox]

> 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.

If you are doing it at boot time as Id expect then you may need to - the SMP
code for bootstrapping has to do pte stuff itself for the same reason

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