linux-kernel - Re: [RFC] Sample kset/ktype/kobject implementation

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Message-ID: <20071130055701.GA3537@darkstar.te-china.tietoenator.com>
Date:	Fri, 30 Nov 2007 13:57:02 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Greg KH <greg@...ah.com>, Cornelia Huck <cornelia.huck@...ibm.com>,
	linux-kernel@...r.kernel.org, Kay Sievers <kay.sievers@...y.org>,
	Jonathan Corbet <corbet@....net>,
	Randy Dunlap <randy.dunlap@...cle.com>, jens.axboe@...cle.com
Subject: Re: [RFC] Sample kset/ktype/kobject implementation

On Fri, Nov 30, 2007 at 01:07:37PM +0800, Dave Young wrote:
> On Nov 30, 2007 6:11 AM, Alan Stern <stern@...land.harvard.edu> wrote:
> > On Thu, 29 Nov 2007, Greg KH wrote:
> >
> > > > > > kobject_put(foo) is needed since it gets you through kobject_cleanup()
> > > > > > where the name can be freed.
> > > > >
> > > > > No, kobject_register() should have handled that for us, right?
> > > >
> > > > kobject_register() doesn't do a kobject_put() if kobject_add() failed.
> > >
> > > Crap.  If I can't get this code right in an example, the API is messed
> > > up.  Time to take Kay seriously and start to revamp the basic kobject
> > > api :)
> >
> > The rule is simple enough.  After calling kobject_register() you should
> > always use kobject_put() -- even if kobject_register() failed.
> >
> > In fact, after calling kobject_init() you should use kobject_put().
> > The first rule follows from this one, since kobject_register() calls
> > kobject_init() internally.
> >
> Hi,
> The behavior is not very clear here, the root problem is that :
> 
> 1. Should we call kobject_put so cleanup work can be done by refcount
> touch zero or call kfree every time after kobject_register failed?
> 
> 2. If kobject_put calling is true, should this be done in
> kobject_register error handling codes or by hand after
> kobject_register failed?
> 
IMO,I'd rather select kobject_put due to the kobj name should also be released.
After searching for kobject_register, I found one leaks as this issue in pktcdvd.

Signed-off-by: Dave Young <hidave.darkstar@...il.com> 

---
drivers/block/pktcdvd.c |    4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff -upr linux/drivers/block/pktcdvd.c linux.new/drivers/block/pktcdvd.c
--- linux/drivers/block/pktcdvd.c	2007-11-30 13:13:44.000000000 +0800
+++ linux.new/drivers/block/pktcdvd.c	2007-11-30 13:24:08.000000000 +0800
@@ -117,8 +117,10 @@ static struct pktcdvd_kobj* pkt_kobj_cre
 	p->kobj.parent = parent;
 	p->kobj.ktype = ktype;
 	p->pd = pd;
-	if (kobject_register(&p->kobj) != 0)
+	if (kobject_register(&p->kobj) != 0) {
+		kobject_put(&p->kobj);
 		return NULL;
+	}
 	return p;
 }
 /*
> Regards
> dave
> > Alan Stern
> >
> >
> >
> > -
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