Re: [PATCH] Fix kunmap() argument in sg_miter_stop

Jens Axboe
2008-11-17T09:00:01Z

On Mon, Nov 17 2008, Ingo Molnar wrote:
>
> * Jens Axboe <jens.axboe@oracle.com> wrote:
>
> > On Mon, Nov 17 2008, Ingo Molnar wrote:
> > >
> > > * Jens Axboe <jens.axboe@oracle.com> wrote:
> > >
> > > > +#define kunmap(p) \
> > > > + do { \
> > > > + struct page *__p; \
> > > > + (void) (&__p == &(p)); \
> > > > + __kunmap(p); \
> > > > + } while (0)
> > > > +
> > > > +#define kunmap_atomic(a, t) \
> > > > + do { \
> > > > + void *__p; \
> > > > + (void) (&__p == &(a)); \
> > > > + __kunmap_atomic(a, t); \
> > > > + } while (0)
> > >
> > > Agreed - but please use the typecheck() primitive. (linux/typecheck.h)
> >
> > Neat, didn't know about that, thanks.
>
> and ack on your patch obviously. Feel free to push it via the block
> tree straight away, it doesnt collide with anything pending in the x86
> tree.
>
> Acked-by: Ingo Molnar <mingo@elte.hu>

The kunmap() bit is easy to do as I mentioned, but the kunmap_atomic()
gets a bit more ugly. Lots of users can just be switched to void *
types, but some get ugly like:

static struct page **shmem_dir_map(struct page *page)
return (struct page **)kmap_atomic(page, KM_USER0);
}

-static inline void shmem_dir_unmap(struct page **dir)
+static inline void shmem_dir_unmap(void *dir)
{
kunmap_atomic(dir, KM_USER0);
}

and others again like fs/exec.c:remove_arg_zero() would really like to
use a char * type since it dereferences it.

I think the kunmap_atomic() change it the most needed part of the patch,
but I don't think it can come for free (eg, we have to add variable to
the above function).

--
Jens Axboe