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

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Message-ID: <20190502083127.GC18363@eros.localdomain>
Date:   Thu, 2 May 2019 18:31:27 +1000
From:   "Tobin C. Harding" <me@...in.cc>
To:     Petr Mladek <pmladek@...e.com>
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, 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 :)

Thanks,
Tobin.