Re: [PATCH 1/2] livepatch: Implement separate coming and going module notifiers

From: Josh Poimboeuf
Date: Fri Jan 29 2016 - 12:30:20 EST


On Fri, Jan 29, 2016 at 05:30:46PM +0100, Miroslav Benes wrote:
> Otherwise than that it looks good. I agree there are advantages to split
> the notifiers. For example we can replace the coming one with the function
> call somewhere in load_module() to improve error handling if the patching
> fails while loading a module. This would be handy with a consistency model
> in the future.

Yeah, we'll need something like that eventually. Though we'll need to
make sure that ftrace_module_enable() is still called beforehand, after
setting MODULE_STATE_COMING state, due to the race described in 5156dca.

Something like:

[note: klp_module_notify_coming() is replaced with klp_module_enable()]

diff --git a/kernel/module.c b/kernel/module.c
index 8358f46..aeabd81 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3371,6 +3371,13 @@ static int complete_formation(struct module *mod, struct load_info *info)
mod->state = MODULE_STATE_COMING;
mutex_unlock(&module_mutex);

+ ftrace_module_enable(mod);
+ err = klp_module_enable(mod);
+ if (err) {
+ ftrace_release_mod(mod);
+ return err;
+ }
+
blocking_notifier_call_chain(&module_notify_list,
MODULE_STATE_COMING, mod);
return 0;
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index eca592f..c42cf37 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5045,9 +5045,6 @@ static int ftrace_module_notify(struct notifier_block *self,
struct module *mod = data;

switch (val) {
- case MODULE_STATE_COMING:
- ftrace_module_enable(mod);
- break;
case MODULE_STATE_GOING:
ftrace_release_mod(mod);
break;

--
Josh