From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from so254-31.mailgun.net ([198.61.254.31]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1knBi6-0007EF-Tb for ath10k@lists.infradead.org; Thu, 10 Dec 2020 02:29:40 +0000 MIME-Version: 1.0 Date: Thu, 10 Dec 2020 10:29:35 +0800 From: Wen Gong Subject: Re: [PATCH v3] ath10k: add flag to protect napi operation to avoid dead loop hang In-Reply-To: <8a97f5ba-8eba-d61b-4c92-bdfd08d388ee@candelatech.com> References: <1598617348-2325-1-git-send-email-wgong@codeaurora.org> <87d02x1rqb.fsf@codeaurora.org> <010101746bd17881-819242de-7cbb-4df3-93e2-59473d281155-000000@us-west-2.amazonses.com> <87r1nzbadn.fsf@codeaurora.org> <8a97f5ba-8eba-d61b-4c92-bdfd08d388ee@candelatech.com> Message-ID: List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "ath10k" Errors-To: ath10k-bounces+kvalo=adurom.com@lists.infradead.org To: Ben Greear Cc: linux-wireless@vger.kernel.org, ath10k@lists.infradead.org, Kalle Valo On 2020-12-09 23:00, Ben Greear wrote: > On 12/9/20 1:24 AM, Kalle Valo wrote: >> Wen Gong writes: >> >>> On 2020-09-08 00:22, Kalle Valo wrote: >>> >>>> Just like with the recent firmware restart patch, isn't >>>> ar->napi_enabled >>>> racy? Wouldn't test_and_set_bit() and test_and_clear_bit() be safer? >>>> >>>> Or are we holding a lock? But then that should be documented with >>>> lockdep_assert_held(). >>> >>> yes, ath10k_hif_start is only called from ath10k_core_start, it has >>> "lockdep_assert_held(&ar->conf_mutex)", and ath10k_hif_stop is only >>> called from ath10k_core_stop, it also has >>> "lockdep_assert_held(&ar->conf_mutex)". then it will not 2 thread >>> both >>> enter ath10k_hif_start/ath10k_hif_stop meanwhile. >> >> Ok, but every function depending on a lock being held should still >> call >> lockdep_assert_held(), that way we can catch the bug if locking >> changes >> later. So it's not enough that ath10k_core_stop() has >> lockdep_assert_held(), also these napi functions should have it. >> >> I actually decided to switch using ATH10K_FLAG_NAPI_ENABLED with >> set_bit() & co, simpler locking that way and no lockdep_assert_held() >> needed anymore. Please check my changes in the pending branch, I have >> only compile tested them: >> >> https://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git/commit/?h=pending&id=e0a466d296bd862080f7796b41349f9f586272c9 >> > > Why do you not need locking? You can't just check a bit is set and > then do work and set > it later without locking, two concurrent CPU threads can pass the > first check and both get into > the logic below it? > maybe because which I said before: ath10k_hif_start is only called from ath10k_core_start, it has "lockdep_assert_held(&ar->conf_mutex)", and ath10k_hif_stop is only called from ath10k_core_stop, it also has "lockdep_assert_held(&ar->conf_mutex)". then it will not 2 thread both enter ath10k_hif_start/ath10k_hif_stop meanwhile. > Thanks, > Ben _______________________________________________ ath10k mailing list ath10k@lists.infradead.org http://lists.infradead.org/mailman/listinfo/ath10k