On Fri, Jan 29, 2016 at 12:40:14PM -0500, Steven Rostedt wrote:
> [ Added Rusty, as he's still maintainer of the module code ]
>
> On Fri, 29 Jan 2016 11:30:10 -0600
> Josh Poimboeuf <jpoim...@redhat.com> wrote:
>
> > 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;
>
> If we end up doing something like this, I would just say punt and have
> the ftrace code be hardcoded into the module code and remove the
> notifiers completely. ftrace (and live kernel patching for that matter)
> are rather special. They are not a filesystem or driver. They are core
> utilities and having them called directly from the module code may be
> prudent and better to understand and control.
Agreed, and we might as well make this change now to avoid more churn
later.
>
> Note, you still need to have prototypes for ftrace_module_enable() and
> a stub when ftrace is not configured. Same goes for klp_module_enable().
>
> -- Steve
>
--
Josh
