Re: [Qemu-devel] [PATCH v2] accel: forbid early use of kvm_enabled() and friends

[Eduardo Habkost <ehabkost@redhat.com>]

On Fri, Jun 29, 2018 at 05:16:52PM -0300, Eduardo Habkost wrote:
> On Fri, Jun 29, 2018 at 05:18:21PM +0200, Igor Mammedov wrote:
> > On Fri, 29 Jun 2018 12:14:05 +0100
> > Daniel P. Berrangé <berrange@redhat.com> wrote:
> > 
> > > On Fri, Jun 29, 2018 at 01:08:38PM +0200, Paolo Bonzini wrote:
> > > > On 29/06/2018 13:07, Greg Kurz wrote:  
> > > > >>>> Also asserting current_machine != NULL is not necessary, since you're
> > > > >>>> immediately dereferencing it.    
> > > > >>> Is there a practical way to simply initialize the accelerators earlier
> > > > >>> in startup sequence, so we just remove or at least reduce, the liklihood
> > > > >>> of accessing it too early ?    
> > > > >> We can try, though not for 3.0 of course.
> > > > >>  
> > > > > FWIW, the motivation for this patch was kvm_enabled() being called under
> > > > > the class_init function of the machine TypeInfo. This happens way earlier
> > > > > than accelerator init. Not sure this is doable, but I can have a look.
> > > > >   
> > > > 
> > > > Probably not, that's way too early indeed.  
> > > 
> > > Yeah, doing anything non-trivial in class_init is just asking for trouble,
> > > as conceivably nothing is initialized at that point. 
> > isn't class_init called lazily? (so it might actually work as far as type
> > isn't touched before kvm is initialized)
> 
> You have a good point: this means class_init bugs won't always
> trigger the assert because of lazy class_init.  It would be a
> good idea to add a functional test that calls qom-list-types
> using --preconfig to try to trigger them.

Heh, I just noticed that the first thing we do immediately after
parsing command-line options is calling:

 select_machine()
 find_default_machine()
 object_class_get_list()
 object_class_foreach()
 g_hash_table_foreach()
 object_class_foreach_tramp()
 type_initialize()

...which will call class_init for every single QOM type in QEMU.

-- 
Eduardo