Re: livepatch: Implement separate coming and going module notifiers

[Jessica Yu]

+++ Josh Poimboeuf [29/01/16 11:30 -0600]:
> 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;
> +	}

If we go this route, should we should print a big warning ("Livepatch
couldn't patch loading module X") instead of aborting the module load
completely? 

> +
> 	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