Return-path: Received: from mail-wi0-f171.google.com ([209.85.212.171]:50123 "EHLO mail-wi0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751146AbaEWJG1 convert rfc822-to-8bit (ORCPT ); Fri, 23 May 2014 05:06:27 -0400 Received: by mail-wi0-f171.google.com with SMTP id cc10so491668wib.4 for ; Fri, 23 May 2014 02:06:26 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <87bnuovq6x.fsf@kamboji.qca.qualcomm.com> References: <1399637749-13489-1-git-send-email-michal.kazior@tieto.com> <1400143324-14911-1-git-send-email-michal.kazior@tieto.com> <1400143324-14911-4-git-send-email-michal.kazior@tieto.com> <87oayovr1m.fsf@kamboji.qca.qualcomm.com> <87bnuovq6x.fsf@kamboji.qca.qualcomm.com> Date: Fri, 23 May 2014 11:06:25 +0200 Message-ID: (sfid-20140523_110633_993738_661A8280) Subject: Re: [PATCH v2 3/5] ath10k: drain tx before restarting hw From: Michal Kazior To: Kalle Valo Cc: "ath10k@lists.infradead.org" , linux-wireless Content-Type: text/plain; charset=UTF-8 Sender: linux-wireless-owner@vger.kernel.org List-ID: On 23 May 2014 10:45, Kalle Valo wrote: > Michal Kazior writes: > >> On 23 May 2014 10:27, Kalle Valo wrote: >>> Michal Kazior writes: >>> >>>> +static void ath10k_drain_tx(struct ath10k *ar) >>>> +{ >>>> + /* workers can hold conf_mutex -- avoid deadlock */ >>>> + WARN_ON(lockdep_is_held(&ar->conf_mutex)); >>> >>> If CONFIG_LOCKDEP is disabled this will fail with: >>> >>> drivers/net/wireless/ath/ath10k/mac.c:2301:2: error: implicit declaration of function 'lockdep_is_held' [-Werror=implicit-function-declaration] >>> >>> I wasn't able to come up with any other way than adding '#ifdef >>> CONFIG_LOCKDEP' which is quite ugly. What should we do? >> >> I guess we could define lockdep_assert_not_held() in debug.h? > > Sure, but I still think it's a bit ugly. The right way to fix this would > be to add it to include/lockdep.h, instead of adding custom checks to a > driver. Good point. I wonder if it's generic enough to justify. > But does this check even make sense? There's nothing preventing > to another thread to take lock just after the WARN_ON(), right? There's nothing wrong with other thread holding it. Actually that's the reason for this very check. The point is to prevent ath10k_drain_tx() being called while caller (current thread) holds conf_mutex. If it were to hold conf_mutex then cancel_work_sync() can deadlock as both workers it tries to stop try to get a hold of the lock too. > Oh, and if we add it to debug.h we should name ath10k_assert_not_held(). > We should not use lockdep's namespace for anything inside ath10k. Good point. Michał