livepatch: Don't block the removal of patches loaded after a forced transition

module_put() is currently never called in klp_complete_transition() when
klp_force is set. As a result, we might keep the reference count even when
klp_enable_patch() fails and klp_cancel_transition() is called.

This might give the impression that a module might get blocked in some
strange init state. Fortunately, it is not the case. The reference count
is ignored when mod->init fails and erroneous modules are always removed.

Anyway, this might be confusing. Instead, this patch moves
the global klp_forced flag into struct klp_patch. As a result,
we block only modules that might still be in use after a forced
transition. Newly loaded livepatches might be eventually completely
removed later.

It is not a big deal. But the code is at least consistent with
the reality.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 6978785bc059c1687b7b76c0a1c5e0159a60a615..6a9165d9b0904d2ace023ff408979090381c4ac1 100644 (file)
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -143,6 +143,7 @@ struct klp_object {
  * @kobj:      kobject for sysfs resources
  * @kobj_added: @kobj has been added and needs freeing
  * @enabled:   the patch is enabled (but operation may be incomplete)
+ * @forced:    was involved in a forced transition
  * @finish:    for waiting till it is safe to remove the patch module
  */
 struct klp_patch {
@@ -155,6 +156,7 @@ struct klp_patch {
        struct kobject kobj;
        bool kobj_added;
        bool enabled;
+       bool forced;
        struct completion finish;
 };
 

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 6f0d9095f662b75b79454a4bbd80dde2849c1170..e77c5017ae0c399a6f1f34e2b00074168648bbbc 100644 (file)
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -45,7 +45,8 @@
  */
 DEFINE_MUTEX(klp_mutex);
 
-static LIST_HEAD(klp_patches);
+/* Registered patches */
+LIST_HEAD(klp_patches);
 
 static struct kobject *klp_root_kobj;
 
@@ -659,6 +660,7 @@ static int klp_init_patch_early(struct klp_patch *patch)
        INIT_LIST_HEAD(&patch->list);
        patch->kobj_added = false;
        patch->enabled = false;
+       patch->forced = false;
        init_completion(&patch->finish);
 
        klp_for_each_object(patch, obj) {

diff --git a/kernel/livepatch/core.h b/kernel/livepatch/core.h
index 48a83d4364cff3c6995025ac6459d04e868f169f..d0cb5390e2476d525dde13f64ac92f963d94ea35 100644 (file)
--- a/kernel/livepatch/core.h
+++ b/kernel/livepatch/core.h
@@ -5,6 +5,7 @@
 #include <linux/livepatch.h>
 
 extern struct mutex klp_mutex;
+extern struct list_head klp_patches;
 
 static inline bool klp_is_object_loaded(struct klp_object *obj)
 {

diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index f27a378ad5e1ea7eb97e24081a29ea85f4ab7b50..a4c921364003aaced3aaf0220f784cbca7beeaca 100644 (file)
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -33,8 +33,6 @@ struct klp_patch *klp_transition_patch;
 
 static int klp_target_state = KLP_UNDEFINED;
 
-static bool klp_forced = false;
-
 /*
  * This work can be performed periodically to finish patching or unpatching any
  * "straggler" tasks which failed to transition in the first attempt.
@@ -137,10 +135,10 @@ static void klp_complete_transition(void)
                  klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
 
        /*
-        * klp_forced set implies unbounded increase of module's ref count if
+        * patch->forced set implies unbounded increase of module's ref count if
         * the module is disabled/enabled in a loop.
         */
-       if (!klp_forced && klp_target_state == KLP_UNPATCHED)
+       if (!klp_transition_patch->forced && klp_target_state == KLP_UNPATCHED)
                module_put(klp_transition_patch->mod);
 
        klp_target_state = KLP_UNDEFINED;
@@ -620,6 +618,7 @@ void klp_send_signals(void)
  */
 void klp_force_transition(void)
 {
+       struct klp_patch *patch;
        struct task_struct *g, *task;
        unsigned int cpu;
 
@@ -633,5 +632,6 @@ void klp_force_transition(void)
        for_each_possible_cpu(cpu)
                klp_update_patch_state(idle_task(cpu));
 
-       klp_forced = true;
+       list_for_each_entry(patch, &klp_patches, list)
+               patch->forced = true;
 }