next-0519 on thinkpad x60: sound related? window manager crash

[Christoph Hellwig]

On Tue, Jun 09, 2020 at 10:05:26AM +0200, Takashi Iwai wrote:
> > >From the disassembly it seems like a vmalloc allocation is NULL, which
> > seems really weird as this patch shouldn't make a difference for them,
> > and I also only see a single places that allocates the field, and that
> > checks for an allocation failure.  But the sound code is a little
> > hard to unwind sometimes.
> 
> It's not clear which sound device being affected, but if it's
> HD-audio on x86, runtime->dma_area points to a vmapped buffer from
> SG-pages allocated by dma_alloc_coherent().
> 
> OTOH, if it's a USB-audio, runtime->dma_area is a buffer by
> vmalloc().

Err, you can't just vmap a buffer returned from dma_alloc_coherent,
dma_alloc_coherent returns values are opaque and can't be used
for virt_to_page.  Whatever that code did has already been broken
per the DMA API contract and on many architectures and just happend
to work on x86 by accident.