From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E03E4C4361B for ; Tue, 15 Dec 2020 08:06:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A97D32228A for ; Tue, 15 Dec 2020 08:06:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726789AbgLOIGb (ORCPT ); Tue, 15 Dec 2020 03:06:31 -0500 Received: from so254-31.mailgun.net ([198.61.254.31]:32314 "EHLO so254-31.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726636AbgLOIGb (ORCPT ); Tue, 15 Dec 2020 03:06:31 -0500 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1608019573; h=Content-Type: MIME-Version: Message-ID: In-Reply-To: Date: References: Subject: Cc: To: From: Sender; bh=EiS56InFbNrrErINtWma1P8wVuX8T9P+uncV9L2GfGc=; b=jMqjs3BpsEp+pP+QDXEpcFpG7tKKRAB9tlmHCe0xVYnaP6RJmCCDPt6Td1scs8pewFGdQ8D5 eiCCb0ajvMteiX7CtOlZkqT4GsDGY4W7w4t+RaFPdgRsibOFmZx2JWr3O6sv6r3/5zthp0pz +u6maHAz0VJwlzWwBAWzUa1u8sc= X-Mailgun-Sending-Ip: 198.61.254.31 X-Mailgun-Sid: WyI3YTAwOSIsICJsaW51eC13aXJlbGVzc0B2Z2VyLmtlcm5lbC5vcmciLCAiYmU5ZTRhIl0= Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n01.prod.us-west-2.postgun.com with SMTP id 5fd86e53f4cc8c621a064f8f (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Tue, 15 Dec 2020 08:05:39 GMT Sender: kvalo=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 5F77AC433C6; Tue, 15 Dec 2020 08:05:39 +0000 (UTC) Received: from potku.adurom.net (88-114-240-156.elisa-laajakaista.fi [88.114.240.156]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: kvalo) by smtp.codeaurora.org (Postfix) with ESMTPSA id A036EC433ED; Tue, 15 Dec 2020 08:05:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org A036EC433ED Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=fail smtp.mailfrom=kvalo@codeaurora.org From: Kalle Valo To: Wen Gong Cc: Ben Greear , linux-wireless@vger.kernel.org, ath10k@lists.infradead.org Subject: Re: [PATCH v3] ath10k: add flag to protect napi operation to avoid dead loop hang 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> Date: Tue, 15 Dec 2020 10:05:35 +0200 In-Reply-To: (Wen Gong's message of "Thu, 10 Dec 2020 10:29:35 +0800") Message-ID: <87tusn1okw.fsf@codeaurora.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org Wen Gong writes: > 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. Yeah, but that was not visible from the code. I now changed the patch in pending branch that this is clearly documented with lockdep_assert_held() and lockdep will warn if someone breaks the locking later on. If a function relies on a lock being held, lockdep_assert_held() needs to be _always_ used to make the locking dependencies clearly visible. -- https://patchwork.kernel.org/project/linux-wireless/list/ https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches