On Tue, Mar 03, 2015 at 06:34:57PM +0100, Petr Mladek wrote:
> Ah, I have missed the comments in the code in the first reply.
> > Why do we need two flags for this? The notifer already
> > sets/clears obj->mod, so can we rely on the value obj->mod to determine
> > if the notifier already ran?
>
> We need this for new patches. There we do not know if the module
> notifier has already been called or not, see also below.
>
> Of course, we might use more optimal storage for the two flags
> if requested. For example, two bits in an unsigned char.
>
>
> > For example:
> >
> > @@ -89,7 +89,7 @@ static bool klp_is_object_loaded(struct klp_object *obj)
> > /* sets obj->mod if object is not vmlinux and module is found */
> > static void klp_find_object_module(struct klp_object *obj)
> > {
> > - if (!klp_is_module(obj))
> > + if (!klp_is_module(obj) || obj->mod)
> > return;
> >
> > mutex_lock(&module_mutex);
> > @@ -98,7 +98,9 @@ static void klp_find_object_module(struct klp_object *obj)
> > * the klp_mutex, which is also taken by the module notifier. This
> > * prevents any module from unloading until we release the klp_mutex.
> > */
> > - obj->mod = find_module(obj->name);
> > + mod = find_module(obj->name);
> > + if (mod->state == MODULE_STATE_LIVE)
>
> The check of the MODULE_STATE_LIVE is not enough. We need to init
> modules when a new patch is registered, the module is still in
> MODULE_STATE_COMING and the module notify handler has already
> been called.
Ok, thanks for explaining. I think I got it now. But the two module
flags aren't ideal.
MODULE_STATE_COMING means that ftrace is already initialized, so I think
it doesn't _have_ to be the notifier which does the work. Instead, can
we just let it be done by whoever gets there first? Like this:
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 01ca088..05390ab 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -89,16 +89,29 @@ static bool klp_is_object_loaded(struct klp_object *obj)
/* sets obj->mod if object is not vmlinux and module is found */
static void klp_find_object_module(struct klp_object *obj)
{
- if (!klp_is_module(obj))
+ struct module *mod;
+
+ if (!klp_is_module(obj) || obj->mod)
return;
mutex_lock(&module_mutex);
+
/*
* We don't need to take a reference on the module here because we have
* the klp_mutex, which is also taken by the module notifier. This
* prevents any module from unloading until we release the klp_mutex.
*/
- obj->mod = find_module(obj->name);
+ mod = find_module(obj->name);
+
+ /*
+ * MODULE_STATE_COMING means we got to the module first before the
+ * notifier did. ftrace is already initialized, so it's fine to go
+ * ahead and start using it.
+ */
+ if (mod->state == MODULE_STATE_COMING ||
+ mod->state == MODULE_STATE_LIVE)
+ obj->mod = mod;
+
mutex_unlock(&module_mutex);
}
@@ -697,8 +710,6 @@ static void klp_free_object_loaded(struct klp_object *obj)
{
struct klp_func *func;
- obj->mod = NULL;
-
for (func = obj->funcs; func->old_name; func++)
func->old_addr = 0;
}
@@ -967,10 +978,31 @@ static int klp_module_notify(struct notifier_block *nb,
unsigned long action,
continue;
if (action == MODULE_STATE_COMING) {
+
+ /*
+ * There's a small window where a register or
+ * enable call may have already done this
+ * initialization. First one there wins.
+ */
+ if (obj->mod)
+ continue;
+
obj->mod = mod;
klp_module_notify_coming(patch, obj);
- } else /* MODULE_STATE_GOING */
+ } else {
+ /* MODULE_STATE_GOING */
+
+ /*
+ * There's a small window where a register or
+ * enable call may have already done this
+ * teardown. First one there wins.
+ */
+ if (!obj->mod)
+ continue;
+
klp_module_notify_going(patch, obj);
+ obj->mod = NULL;
+ }
break;
}
--
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