Re: modules: set mod->state to GOING before going notifiers are called

[Jessica Yu]

+++ Rusty Russell [10/03/16 13:57 +1030]:
> Jessica Yu <jeyu@xxxxxxxxxx> writes:
> > In load_module(), the going notifiers are called during error handling
> > when an error occurs after the coming notifiers have already been called.
> > However, a module's state is still MODULE_STATE_COMING when the going
> > notifiers are called in the error path. To be consistent, also set
> > mod->state to MODULE_STATE_GOING before calling the going notifiers.
> >
> > Signed-off-by: Jessica Yu <jeyu@xxxxxxxxxx>
> > ---
> >  kernel/module.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/kernel/module.c b/kernel/module.c
> > index 1981ae0..9e80576 100644
> > --- a/kernel/module.c
> > +++ b/kernel/module.c
> > @@ -3494,6 +3494,9 @@ static int load_module(struct load_info *info, const char __user *uargs,
> >  	return do_init_module(mod);
> >
> >   coming_cleanup:
> > +	mutex_lock(&module_mutex);
> > +	mod->state = MODULE_STATE_GOING;
> > +	mutex_unlock(&module_mutex);
> >  	blocking_notifier_call_chain(&module_notify_list,
> >  				     MODULE_STATE_GOING, mod);
>
> Actually, reviewing this patch makes me realize it is wrong.
>
> We rely on the state of the module being MODULE_STATE_COMING here:
>
>        static inline int strong_try_module_get(struct module *mod)
>        {
>        	BUG_ON(mod && mod->state == MODULE_STATE_UNFORMED);
>        	if (mod && mod->state == MODULE_STATE_COMING)
>                	return -EBUSY;
>
> We will just have to document that the notifier can be called with
> a module in MODULE_STATE_COMING if it never succeeded its
> initialization.

Ah, thanks for catching that. I think I remember seeing this conditional and
assuming it wouldn't be a problem since GOING modules would fail in
try_module_get() (as it is does not pass the module_is_live() test) and
subsequently strong_try_module_get() would also fail.. But, I think I ought to
review how module states interact before making a change like this, so, please
ignore this patch.

Jessica