Re: [PATCH] static_call: Handle module init failure correctly in static_call_del_module()

[Christophe Leroy]

Hi Luis,

Le 24/09/2024 à 09:22, Mike Rapoport a écrit :
> On Thu, Sep 19, 2024 at 02:53:34AM -0700, Luis Chamberlain wrote:
> > On Fri, Sep 06, 2024 at 04:24:56PM -0700, Luis Chamberlain wrote:
> > > On Thu, Sep 05, 2024 at 11:44:00AM +0200, Thomas Gleixner wrote:
> > > > Now you at least provided the information that the missing cleanup in
> > > > the init() function is not the problem. So the obvious place to look is
> > > > in the module core code whether there is a failure path _after_
> > > > module->init() returned success.
> > > >
> > > > do_init_module()
> > > >          ret = do_one_initcall(mod->init);
> > > >          ...
> > > > 	ret = module_enable_rodata_ro(mod, true);
> > > > 	if (ret)
> > > > 		goto fail_mutex_unlock;
> > > >
> > > > and that error path does _not_ invoke module->exit(), which is obviously
> > > > not correct. Luis?
> > >
> > > You're spot on this needs fixing.
> >
> > Christophe, this is a regression caused by the second hunk of your commit
> > d1909c0221739 ("module: Don't ignore errors from set_memory_XX()") on v6.9.
> > Sadly there are a few issues with trying to get to call mod->exit():
> >
> > - We should try try_stop_module()  and that can fail
> > - source_list may not be empty and that would block removal
> > - mod->exit may not exist
> >
> > I'm wondering if instead we should try to do the module_enable_rodata_ro()
> > before the init, but that requires a bit more careful evaluation...
>
> There is ro_after_init section, we can't really make it RO before ->init()
>   

Surprisingly I never received Luis's email allthough I got this answer 
from Mike that I overlooked.

So coming back here from 
https://lore.kernel.org/all/ZyQhbHxDTRXTJgIx@xxxxxxxxxxxxxxxxxxxxxx/

As far as I understand, indeed once init is called it is too late to 
fail, right ? Especially when the module has no exit() path or when 
CONFIG_MODULE_UNLOAD is not built in.

So the only thing we can do then is a big fat warning telling 
set_memory_ro() on ro_after_init memory has failed ?

Maybe we should try and change it to RO then back to RW before calling 
init, to be on a safer side hopping that if change to RO works once it 
will work twice ?

Christophe