linux-kernel - Re: [PATCH 1/11] kernel/kfifo.c: trivial: use BUG

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Date:	Tue, 2 Aug 2011 13:52:49 +0200 (CEST)
From:	Julia Lawall <julia@...u.dk>
To:	Andrea Righi <arighi@...eler.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, trivial@...nel.org,
	kernel-janitors@...r.kernel.org,
	Stefani Seibold <stefani@...bold.net>,
	"Ira W. Snyder" <iws@...o.caltech.edu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/11] kernel/kfifo.c: trivial: use BUG_ON

On Tue, 2 Aug 2011, Andrea Righi wrote:

> On Tue, Aug 02, 2011 at 12:34:54PM +0200, Julia Lawall wrote:
> > From: Julia Lawall <julia@...u.dk>
> > 
> > Use BUG_ON(x) rather than if(x) BUG();
> > 
> > The semantic patch that fixes this problem is as follows:
> > (http://coccinelle.lip6.fr/)
> > 
> > // <smpl>
> > @@ identifier x; @@
> > -if (x) BUG();
> > +BUG_ON(x);
> > 
> > @@ identifier x; @@
> > -if (!x) BUG();
> > +BUG_ON(!x);
> > // </smpl>
> > 
> > Signed-off-by: Julia Lawall <julia@...u.dk>
> > 
> 
> The patch looks good. However, I think we should just get rid of the
> BUG_ON() there. If nents is 0, setup_sgl_buf() would just returns 0 and
> nothing critical will happen.

I don't know the code at all.  Indeed, I'm not sure to see any uses of eg 
__kfifo_dma_in_prepare_r, except in demo code.  But that would imply 
returning 0 for two different reasons: asking for nothing and being out of 
space.

julia

> Also consider that in __kfifo_dma_in_prepare(), the equivalent of
> __kfifo_dma_in_prepare_r() when recsize is 0, we don't check nents at
> all.
> 
> -Andrea
> 
> > ---
> >  kernel/kfifo.c |    6 ++----
> >  1 file changed, 2 insertions(+), 4 deletions(-)
> > 
> > diff -u -p a/kernel/kfifo.c b/kernel/kfifo.c
> > --- a/kernel/kfifo.c
> > +++ b/kernel/kfifo.c
> > @@ -562,8 +562,7 @@ EXPORT_SYMBOL(__kfifo_to_user_r);
> >  unsigned int __kfifo_dma_in_prepare_r(struct __kfifo *fifo,
> >  	struct scatterlist *sgl, int nents, unsigned int len, size_t recsize)
> >  {
> > -	if (!nents)
> > -		BUG();
> > +	BUG_ON(!nents);
> >  
> >  	len = __kfifo_max_r(len, recsize);
> >  
> > @@ -586,8 +585,7 @@ EXPORT_SYMBOL(__kfifo_dma_in_finish_r);
> >  unsigned int __kfifo_dma_out_prepare_r(struct __kfifo *fifo,
> >  	struct scatterlist *sgl, int nents, unsigned int len, size_t recsize)
> >  {
> > -	if (!nents)
> > -		BUG();
> > +	BUG_ON(!nents);
> >  
> >  	len = __kfifo_max_r(len, recsize);
> >  
> --
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