Re: Linux-2.6.12

[Richard B. Johnson]

On Mon, 20 Jun 2005, Hugh Dickins wrote:

> Gosh, I thought from the Subject that you'd taken over from Linus,
> and were announcing your new release ;)
>
> On Mon, 20 Jun 2005, Richard B. Johnson wrote:
> > Attempts to run a driver that worked up to 2.6.11.9 shows that
> > it aparently is no longer possible to nest calls to `down`.
> > In other words, a procedure that has taken a semaphore can't
> > then take another semaphore.
> >
> > down(&first_resource);
> > down(&second_resource);
> > ...
> > ...
> > up(&second_resource);
> > up(&first_resource);
> >
> >
> > The error is 'sleeping function called from invalid context....'
> >
> > ------------[ cut here ]------------
> > kernel BUG at mm/memory.c:1112!
>
> No, the error is "kernel BUG at mm/memory.c:1112!", which occurs while
> it's holding page table lock, from which it doesn't recover very well.
>
> It's the BUG_ON(!pte_none(*pte)) in remap_pte_range.  Maybe your page
> table is corrupt, maybe your driver is trying to remap_pfn_range on
> top of something already mapped.
>
> Hugh

But of course it is. There is some memory that is mapped into the
driver's address space, used for DMA. It was obtained using
ioremap_nocache(). This memory is then mapped into user-space
when the user executes mmap(). This is how we DMA directly to
user-space. Is this no longer allowed?


Cheers,
Dick Johnson
Penguin : Linux version 2.6.12 on an i686 machine (5537.79 BogoMips).
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