linux-kernel - Re: [PATCH 10/14] scsi: osd: fix device

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Message-ID: <20100919143948.GA4866@albatros>
Date:	Sun, 19 Sep 2010 18:39:50 +0400
From:	Vasiliy Kulikov <segooon@...il.com>
To:	Dan Carpenter <error27@...il.com>, kernel-janitors@...r.kernel.org,
	Boaz Harrosh <bharrosh@...asas.com>,
	Benny Halevy <bhalevy@...asas.com>,
	"James E.J. Bottomley" <James.Bottomley@...e.de>,
	Tejun Heo <tj@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	osd-dev@...n-osd.org, linux-scsi@...r.kernel.org,
	cornelia.huck@...ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/14] scsi: osd: fix device_register() error handling

On Sun, Sep 19, 2010 at 16:26 +0200, Dan Carpenter wrote:
> On Sun, Sep 19, 2010 at 04:55:07PM +0400, Vasiliy Kulikov wrote:
> > If device_register() fails then call put_device().
> > See comment to device_register.
> > 
> > Signed-off-by: Vasiliy Kulikov <segooon@...il.com>
> > ---
...
> 
> Hm...  So if device_register() fails then we should always call
> device_put()?  It seems like a lot of existing code does that but I
> hadn't realized until now that that is how it works.

Yes, almost ALL code using device_register() is buggy :-(

> Why can't the device_put() just be added inside the device_register() so
> the unwinding works automatically?

Because some code already calls device_put().  Also it is documented like
not putting the device.  However, I'm in doubt why it is written this way.

> Also if someone add some more stuff to the end of this function, will
> the device_unregister() followed by a device_put() cause problems if we
> unwind like this?

Yes, device_register() gets one reference, you should put in in both cases -
when device_register() failed and when it succeeded, but only one time.
device_unregister() puts it, so it is "double putting".

> +err_free_something:
> +	kfree(foo);
> +	device_unregister(&oud->class_dev);
> > +err_put_device:
> > +	put_device(&oud->class_dev);
> >  err_put_cdev:
> >  	cdev_del(&oud->cdev);
> >  err_put_disk:
> 
> If that's the case then the put_device() should be called infront of the
> goto.

As it is the last call that may fail, it is redundant.  Or you mean for future,
if someone adds more code after device_register()?

 
Thanks,
-- 
Vasiliy
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