Re: [PATCH 2/2] livepatch: Use correct kobject cleanup function

From: "Tobin C. Harding" <me@tobin.cc>
To: Petr Mladek <pmladek@suse.com>
Cc: "Tobin C. Harding" <tobin@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Jiri Kosina <jikos@kernel.org>, Miroslav Benes <mbenes@suse.cz>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] livepatch: Use correct kobject cleanup function
Date: Wed, 1 May 2019 07:37:30 +1000	[thread overview]
Message-ID: <20190430213730.GC9454@eros.localdomain> (raw)
In-Reply-To: <20190430150811.4hzhtz4w46o6numh@pathway.suse.cz>

On Tue, Apr 30, 2019 at 05:08:11PM +0200, Petr Mladek wrote:
> On Tue 2019-04-30 10:15:34, Tobin C. Harding wrote:
> > The correct cleanup function after a call to kobject_init_and_add() has
> > succeeded is kobject_del() _not_ kobject_put().  kobject_del() calls
> > kobject_put().
> 
> Really? I see only kobject_put(kobj->parent) in kobject_del.
> It decreases a reference of the _parent_ object and not
> the given one.

Thanks Petr, you are right.  I misread kobject_del().  The story
thickens, so we need to call kobject_del() AND kobject_put().

> Also the section "Kobject removal" in Documentation/kobject.txt
> says that kobject_del() is for two-stage removal. kobject_put()
> still needs to get called at a later time.

Is this call sequence above what is meant by 'two-stage removal', I
didn't really understand that bit of the docs (and I almost always just
assume docs are stale and take them as a hint only :)

> IMHO, this patch causes that kobject_put() would never get called.

I'll do a v2 of this one and re-check all the patches on this I've
already sent (including the docs ones).

> That said, we could probably make the removal a bit cleaner
> by using kobject_del() in klp_free_patch_start() and
> kobject_put() in klp_free_patch_finish(). But I have
> to think more about it.

Noted, thanks for your review.

	Tobin