linux-kernel - Re: [PATCHv4 10/17] pps: use BUG_ON for kernel API safety checks

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Message-ID: <20101121084218.GP13356@enneenne.com>
Date:	Sun, 21 Nov 2010 09:42:19 +0100
From:	Rodolfo Giometti <giometti@...eenne.com>
To:	Alexander Gordeev <lasaine@....cs.msu.su>
Cc:	Joe Perches <joe@...ches.com>, linux-kernel@...r.kernel.org,
	"Nikita V. Youshchenko" <yoush@...msu.su>,
	linuxpps@...enneenne.com, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCHv4 10/17] pps: use BUG_ON for kernel API safety checks

On Sun, Nov 21, 2010 at 03:40:08AM +0300, Alexander Gordeev wrote:
> ?? Sat, 20 Nov 2010 09:01:41 -0800
> Joe Perches <joe@...ches.com> ??????????:
> 
> > On Sat, 2010-11-20 at 17:13 +0100, Rodolfo Giometti wrote:
> > > On Thu, Nov 18, 2010 at 07:01:03PM +0300, Alexander Gordeev wrote:
> > > > This way less overhead is involved when running production kernel.
> > > > If you want to debug a pps client module please define DEBUG to enable
> > > > the checks.
> > > > Signed-off-by: Alexander Gordeev <lasaine@....cs.msu.su>
> > []
> > > > diff --git a/drivers/pps/kapi.c b/drivers/pps/kapi.c
> > > > @@ -179,10 +168,8 @@ void pps_event(struct pps_device *pps, struct pps_event_time *ts, int event,
> > > >  	int captured = 0;
> > > >  	struct pps_ktime ts_real;
> > > >  
> > > > -	if ((event & (PPS_CAPTUREASSERT | PPS_CAPTURECLEAR)) == 0) {
> > > > -		dev_err(pps->dev, "unknown event (%x)\n", event);
> > > > -		return;
> > > > -	}
> > > > +	/* check event type */
> > > > +	BUG_ON((event & (PPS_CAPTUREASSERT | PPS_CAPTURECLEAR)) == 0);
> > > 
> > > Ack.
> > > 
> > > This is a correct usage of BUG_ON. :)
> > 
> > I don't think that's true.
> > 
> > /*
> >  * Don't use BUG() or BUG_ON() unless there's really no way out; one
> >  * example might be detecting data structure corruption in the middle
> >  * of an operation that can't be backed out of.  If the (sub)system
> >  * can somehow continue operating, perhaps with reduced functionality,
> >  * it's probably not BUG-worthy.
> >  *
> >  * If you're tempted to BUG(), think again:  is completely giving up
> >  * really the *only* solution?  There are usually better options, where
> >  * users don't need to reboot ASAP and can mostly shut down cleanly.
> >  */
> 
> Hmm, didn't check that before. What is more appropriate in this
> situation?

IMHO here you can use BUG_ON() but not into pps_register_source().

Ciao,

Rodolfo

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