Re: [PATCH 0/4] revert the commit 22a9189f (cdrom: use kmalloced buffers instead of buffers on stack)

David Miller
2008-05-22T01:18:52Z

From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Date: Thu, 22 May 2008 10:13:31 +0900

> DMA on stack is forbidden because of non coherent architecutes and
> architectures can't uses stack addresses for DMA? What architectures
> can't uses stack addresses for DMA? Would it be better to just forbid
> using stack addresses for DMA on all the architectures at all times?

Rather, the real problem is that some architectures map the kernel
stack virtually, and as a result virt_to_page() and things like that
will not work.

It really is fully not working to put DMA buffers on the stack
in these cases.