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

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Date:   Thu, 2 May 2019 10:51:27 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     "Tobin C. Harding" <me@...in.cc>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "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 2019-05-02 18:31:27, Tobin C. Harding wrote:
> 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().
> > 
> > Anyway, the right solution is to call kobject_init()
> > already in klp_init_patch_early() for the statically
> > defined structures and in klp_alloc*() for the dynamically
> > allocated ones. Then we could simply call kobject_put()
> > every time.
> > 
> > Tobin, this goes deeper into the livepatching code that
> > you probably expected. Do you want to do the above
> > suggested change or should I prepare the patch?
> 
> I'd love for you to handle this one Petr, I'd say its a net gain
> time wise that way since if I do it you'll have to review it too
> carefully anyways.
> 
> So that will mean patch #1 and #5 of this series are dropped and handed
> off to you (thanks).  Patch #2 and #3 Greg said he will take.  Patch #4
> is not needed.  That's a win in my books :)

Sound like a great plan. I am going to work on the patch for
the livepatching code.

Anyway, thanks a lot for your patches. It is a big relief to realize
that we could remove some hacks and do it clearly, modulo the static
structures ;-)

Best Regards,
Petr