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 for ath10k@lists.infradead.org; Mon, 23 Jun 2014 11:51:54 +0000
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Subject: Re: [PATCH 2/2] ath10k: make core registering async
From: Johannes Berg <johannes@sipsolutions.net>
Date: Mon, 23 Jun 2014 13:51:18 +0200
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To: Michal Kazior <michal.kazior@tieto.com>
Cc: linux-wireless <linux-wireless@vger.kernel.org>, "ath10k@lists.infradead.org" <ath10k@lists.infradead.org>

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


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