linux-kernel - Re: [RFC PATCH 5/5] livepatch: Do not manually track kobject initialization

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Date:   Thu, 2 May 2019 09:42:30 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     "Tobin C. Harding" <tobin@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 5/5] livepatch: Do not manually track kobject
 initialization

On Thu, May 02, 2019 at 09:30:44AM +0200, Petr Mladek wrote:
> On Thu 2019-05-02 09:12:32, Greg Kroah-Hartman wrote:
> > On Thu, May 02, 2019 at 12:31:42PM +1000, Tobin C. Harding wrote:
> > > Currently we use custom logic to track kobject initialization.  Recently
> > > a predicate function was added to the kobject API so we now no longer
> > > need to do this.
> > > 
> > > Use kobject API to check for initialized state of kobjects instead of
> > > using custom logic to track state.
> > > 
> > > Signed-off-by: Tobin C. Harding <tobin@...nel.org>
> > > ---
> > >  include/linux/livepatch.h |  6 ------
> > >  kernel/livepatch/core.c   | 18 +++++-------------
> > >  2 files changed, 5 insertions(+), 19 deletions(-)
> > > 
> > > @@ -626,7 +626,7 @@ static void __klp_free_objects(struct klp_patch *patch, bool nops_only)
> > >  		list_del(&obj->node);
> > >  
> > >  		/* Might be called from klp_init_patch() error path. */
> > > -		if (obj->kobj_added) {
> > > +		if (kobject_is_initialized(&obj->kobj)) {
> > >  			kobject_put(&obj->kobj);
> > >  		} else if (obj->dynamic) {
> > >  			klp_free_object_dynamic(obj);
> > 
> > Same here, let's not be lazy.
> > 
> > The code should "know" if the kobject has been initialized or not
> > because it is the entity that asked for it to be initialized.  Don't add
> > extra logic to the kobject core (like the patch before this did) just
> > because this one subsystem wanted to only write 1 "cleanup" function.
> 
> We use kobject for a mix of statically and dynamically defined
> structures[*]. And we misunderstood the behavior of kobject_init().

Eeek, no, a kobject should never be used for a static structure, that's
just wrong.

Well, almost wrong, ignore how the driver core itself does this in
places :)

thanks,

greg k-h