linux-kernel - Re: [PATCH] Fix kunmap() argument in sg_miter

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Date:	Mon, 17 Nov 2008 09:58:07 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Tejun Heo <htejun@...il.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Hugh Dickins <hugh@...itas.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] Fix kunmap() argument in sg_miter_stop

On Mon, Nov 17 2008, Ingo Molnar wrote:
> 
> * Jens Axboe <jens.axboe@...cle.com> wrote:
> 
> > On Mon, Nov 17 2008, Ingo Molnar wrote:
> > > 
> > > * Jens Axboe <jens.axboe@...cle.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@...e.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

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