On Tue, Mar 10, 2015 at 01:01:07PM +0100, Petr Mladek wrote:
> On Mon 2015-03-09 09:40:55, Josh Poimboeuf wrote:
> > On Mon, Mar 09, 2015 at 02:25:28PM +0100, Petr Mladek wrote:
> > > +
> > > mutex_unlock(&module_mutex);
> > > }
> > >
> > > @@ -736,6 +748,7 @@ static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
> > > return -EINVAL;
> > >
> > > obj->state = KLP_DISABLED;
> > > + obj->mod = NULL;
> > >
> > > klp_find_object_module(obj);
> > >
> > > @@ -926,6 +939,15 @@ static int klp_module_notify(struct notifier_block *nb, unsigned long action,
> > >
> > > mutex_lock(&klp_mutex);
> > >
> > > + /*
> > > + * Each module has to know that the notifier has been called.
> > > + * We never know what module will get patched by a new patch.
> > > + */
> > > + if (action == MODULE_STATE_COMING)
> > > + mod->klp_alive = true;
> > > + else /* MODULE_STATE_GOING */
> > > + mod->klp_alive = false;
> > > +
> >
> > Any reason why this needs to be protected by the mutex?
>
> We need to synchronize it with the check in
> klp_find_object_module(). Otherwise, for example, the check might read
> "true" and add/enable new patch but this notify handler will be
> blocked until the patch is added => it will mess the order of
> patches.
>
> It might be more clean to take module_mutex here but the value is
> needed only by livepatching, so klp_mutex seems to be enough.
Ah, right. Looks good to me.
> > > list_for_each_entry(patch, &klp_patches, list) {
> > > for (obj = patch->objs; obj->funcs; obj++) {
> > > if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
> > > diff --git a/kernel/module.c b/kernel/module.c
> > > index d856e96a3cce..b3ffc231ce0d 100644
> > > --- a/kernel/module.c
> > > +++ b/kernel/module.c
> > > @@ -3271,6 +3271,10 @@ static int load_module(struct load_info *info, const char __user *uargs,
> > > }
> > > #endif
> > >
> > > +#ifdef CONFIG_LIVEPATCH
> > > + mod->klp_alive = false;
> > > +#endif
> > > +
> >
> > I don't think you need this initialization. It looks like the module
> > struct is embedded in the mod->module_core region which is initialized
> > to zero in move_module().
>
> I have looked at this before but I was not able to find a code
> zeroing struct module. If I get it correctly, mod->module_core
> is a location where symbol table sections are copied or so.
Yeah, it's far from obvious. AFAICT, it's cleared by the
"memset(ptr, 0, mod->core_size)" line.
--
Josh
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