[RFC PATCH 8/9] livepatch: allow patch modules to be removed

[Josh Poimboeuf <jpoimboe@redhat.com>]

Now that we have a consistency model we can detect when unpatching is
complete and the patch module can be safely removed.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 kernel/livepatch/core.c       | 25 ++++---------------------
 kernel/livepatch/transition.c |  3 +++
 2 files changed, 7 insertions(+), 21 deletions(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 790dc10..e572523 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -352,6 +352,9 @@ static int __klp_enable_patch(struct klp_patch *patch)
 	    !list_prev_entry(patch, list)->enabled)
 		return -EBUSY;
 
+	if (!try_module_get(patch->mod))
+		return -ENODEV;
+
 	pr_notice_once("tainting kernel with TAINT_LIVEPATCH\n");
 	add_taint(TAINT_LIVEPATCH, LOCKDEP_STILL_OK);
 
@@ -497,10 +500,6 @@ static struct attribute *klp_patch_attrs[] = {
 
 static void klp_kobj_release_patch(struct kobject *kobj)
 {
-	/*
-	 * Once we have a consistency model we'll need to module_put() the
-	 * patch module here.  See klp_register_patch() for more details.
-	 */
 }
 
 static struct kobj_type klp_ktype_patch = {
@@ -715,29 +714,13 @@ EXPORT_SYMBOL_GPL(klp_unregister_patch);
  */
 int klp_register_patch(struct klp_patch *patch)
 {
-	int ret;
-
 	if (!klp_initialized())
 		return -ENODEV;
 
 	if (!patch || !patch->mod)
 		return -EINVAL;
 
-	/*
-	 * A reference is taken on the patch module to prevent it from being
-	 * unloaded.  Right now, we don't allow patch modules to unload since
-	 * there is currently no method to determine if a thread is still
-	 * running in the patched code contained in the patch module once
-	 * the ftrace registration is successful.
-	 */
-	if (!try_module_get(patch->mod))
-		return -ENODEV;
-
-	ret = klp_init_patch(patch);
-	if (ret)
-		module_put(patch->mod);
-
-	return ret;
+	return klp_init_patch(patch);
 }
 EXPORT_SYMBOL_GPL(klp_register_patch);
 
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index 2630296..20fafd2 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -54,6 +54,9 @@ void klp_complete_transition(void)
 		for (func = obj->funcs; func->old_name; func++)
 			func->transition = 0;
 
+	if (klp_universe_goal == KLP_UNIVERSE_OLD)
+		module_put(klp_transition_patch->mod);
+
 	klp_transition_patch = NULL;
 }
 
-- 
2.1.0