Date:   Thu, 2 Feb 2023 11:14:15 +0100
From:   Petr Mladek <pmladek@suse.com>
To:     Josh Poimboeuf <jpoimboe@kernel.org>
Cc:     Marcos Paulo de Souza <mpdesouza@suse.com>,
        linux-kernel@vger.kernel.org, live-patching@vger.kernel.org,
        jpoimboe@redhat.com, joe.lawrence@redhat.com
Subject: Re: [PATCH v2 4/4] livepatch/shadow: Add garbage collection of
 shadow variables
Message-ID: <Y9uM94UOJWcNxnkI@alley>
References: <20221026194122.11761-1-mpdesouza@suse.com>
 <20221026194122.11761-5-mpdesouza@suse.com>
 <20230201001817.ej7n3ehtgaxwr3pq@treble>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230201001817.ej7n3ehtgaxwr3pq@treble>
Precedence: bulk

On Tue 2023-01-31 16:18:17, Josh Poimboeuf wrote:
> On Wed, Oct 26, 2022 at 04:41:22PM -0300, Marcos Paulo de Souza wrote:
> > The shadow variable type might then be added into a new @shadow_types
> > member of struct klp_object. They will get then automatically registered
> > and unregistered when the object is being livepatched. The registration
> > increments the reference count. Unregistration decreases the reference
> > count. All shadow variables of the given type are freed when the reference
> > count reaches zero.
> 
> How does the automatic unregistration work for replaced patches?
> 
> I see klp_unpatch_replaced_patches() is called, but I don't see where it
> ends up calling klp_shadow_unregister() for the replaced patch(es).

Great catch! I forgot that replaced patches are handled separately.
We should do the following (on top of this patch):

--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -123,8 +123,11 @@ static void klp_complete_transition(void)
 			continue;
 		if (klp_target_state == KLP_PATCHED)
 			klp_post_patch_callback(obj);
-		else if (klp_target_state == KLP_UNPATCHED) {
+		else if (klp_target_state == KLP_UNPATCHED)
 			klp_post_unpatch_callback(obj);
+
+		if (klp_target_state == KLP_UNPATCHED ||
+		    klp_transition_patch->replace) {
 			klp_unregister_shadow_types(obj);
 		}
 	}


Also we should add more selftests for handling the shadow variables.

Best Regards,
Petr