Re: [KJ][PATCH] Correct misc_register return code handling in several drivers

On Wed, Oct 25, 2006 at 08:42:42AM +1000, Benjamin Herrenschmidt wrote:
On Tue, 2006-10-24 at 08:53 -0400, Neil Horman wrote:
On Tue, Oct 24, 2006 at 01:34:34PM +1000, Benjamin Herrenschmidt wrote:
On Mon, 2006-10-23 at 13:19 -0400, Neil Horman wrote:
Hey All-
Janitor patch to clean up return code handling and exit from failed
calls to misc_register accross several modules.

The patch doesn't match the description... What are those INIT_LIST_HEAD
things ? Is this something I've missed or is this a new requirement for
all misc devices ? Can't it be statically initialized instead ?


The INIT_LIST_HEAD is there to prevent a potential oops on module removal.
misc_register, if it fails, leaves miscdevice.list unchanged. That means its
next and prev pointers contain NULL or garbage, when both pointers should contain
&miscdevice.list. If we don't do that, then there is a chance we will oops on
module removal when we do a list_del in misc_deregister on the moudule_exit
routine. I could have done this statically, but I thought it looked cleaner to
do it with the macro in the code.

Hrm... I see, but I still for some reason don't like it that much.. I'd
rather have misc_register() do the initialisation unconditionally before
it can fail, don't you think ?

We would theorically have a similar problem with any driver that does


xxxx_register(&static_struct)

and

xxxx_unregister(&static_struct)

(pci, usb, etc...)

As long as there are list heads involved. I think the proper solution
here is to have either the unregister be smart and test for NULL/NULL or
the register initialize those fields before it has a chance to fail.

Ben.


I agreed with you in my last note regarding this, I think moving the
INIT_LIST_HEAD inside the misc_register function is a good idea, but since this
is a cleanup patch with several other fixups in it, I'd just as soon get this
integrated, and make that change in a separate patch.

Regards
Neil

--
/***************************************************
*Neil Horman
*Software Engineer
*gpg keyid: 1024D / 0x92A74FA1 - http://pgp.mit.edu
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