Message-ID: <1403524278.4418.19.camel@jlt4.sipsolutions.net> (sfid-20140623_135133_765801_F26B0E6D)
Subject: Re: [PATCH 2/2] ath10k: make core registering async
From: Johannes Berg <johannes@sipsolutions.net>
To: Michal Kazior <michal.kazior@tieto.com>
Cc: "ath10k@lists.infradead.org" <ath10k@lists.infradead.org>,
	linux-wireless <linux-wireless@vger.kernel.org>
Date: Mon, 23 Jun 2014 13:51:18 +0200
In-Reply-To: <CA+BoTQk=DU=-HzVo-XsQTpCt6CS7aXxQMy5hTyQ7qC56ebBLZQ@mail.gmail.com> (sfid-20140623_121907_420359_3A843E5E)
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Hi,

>  [worker]
>  complete_all()
>  device_release_driver()
>  dev_lock()
>  {already held, yield}
>  [syscall]
>  free(internal structures)
>  dev_unlock()
>  return
>  [worker]
>  {woken up, but dev->driver == NULL so no callbacks}
>  dev_unlock()
>  return
> 
> The driver code section may not be reachable anymore upon worker
> returning from the device_release_driver() call, right? Also since
> ath10k uses an internal worker it also means the work_struct would be
> already freed by the syscall flow (i.e. worker would run after driver
> has supposedly been cleaned up..). Even if ath10k was to use
> request_firmware_nowait(), which allocates a temporary work_struct,
> the unreachable code section still remains a problem.
> 
> Or maybe this isn't really a problem and/or I'm missing something?

Yeah, hmm, this looks like a problem. I guess we didn't really consider
module unload in such detail ...

I guess this would crash upon return from device_release_driver()? I
guess if that's the last thing then maybe we'd actually get a tail-call
optimisation, but we don't want to rely on that of course!

Seems like to fix it we just need to get a module reference though? Can
a module put() itself though? Hmmm.

johannes