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

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Date:   Fri, 6 Aug 2021 15:51:31 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Kefeng Wang <wangkefeng.wang@...wei.com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        hannes@...essinduktion.org, davem@...emloft.net,
        akpm@...ux-foundation.org, Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Minmin chen <chenmingmin@...wei.com>
Subject: Re: [PATCH v2] once: Fix panic when module unload

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@huawei.com/
> 
> 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.

Sure, I trust you :)