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

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Message-ID: <1290272501.27951.27.camel@Joe-Laptop>
Date:	Sat, 20 Nov 2010 09:01:41 -0800
From:	Joe Perches <joe@...ches.com>
To:	Rodolfo Giometti <giometti@...eenne.com>
Cc:	Alexander Gordeev <lasaine@....cs.msu.su>,
	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 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.
 */


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