Re: [PATCH v2] once: Fix panic when module unload

[Kefeng Wang]

On 2021/8/6 21:51, Greg KH wrote:
> On Fri, Aug 06, 2021 at 06:43:28AM -0700, Jakub Kicinski wrote:
> > On Fri, 6 Aug 2021 16:21:24 +0800 Kefeng Wang wrote:
> > > DO_ONCE
> > > DEFINE_STATIC_KEY_TRUE(___once_key);
> > > __do_once_done
> > >    once_disable_jump(once_key);
> > >      INIT_WORK(&w->work, once_deferred);
> > >      struct once_work *w;
> > >      w->key = key;
> > >      schedule_work(&w->work);                     module unload
> > >                                                     //*the key is
> > > destroy*
> > > process_one_work
> > >    once_deferred
> > >      BUG_ON(!static_key_enabled(work->key));
> > >         static_key_count((struct static_key *)x)    //*access key, crash*
> > >
> > > When module uses DO_ONCE mechanism, it could crash due to the above
> > > concurrency problem, we could reproduce it with link[1].
> > >
> > > Fix it by add/put module refcount in the once work process.
> > >
> > > [1] https://lore.kernel.org/netdev/eaa6c371-465e-57eb-6be9-f4b16b9d7cbf@xxxxxxxxxx/
> > Seems reasonable. Greg does it look good to you?
> Me?  I was not paying attention to this at all, sorry...
>
> > I think we can take it thru networking since nobody cared to pick up v1.
Thanks all ;)
> Sure, I trust you :)
> .