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=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 BDEF6C433E3 for ; Thu, 23 Jul 2020 00:37:27 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8A385207BB for ; Thu, 23 Jul 2020 00:37:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Xlj2lEDj"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="IHz98g6h" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8A385207BB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:Message-ID:References:In-Reply-To:Subject:To:From: Date:MIME-Version:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Iypvu2hYPV9Y3NFfrjseOba9htIkM+XtYZU3vygrBHE=; b=Xlj2lEDjaVwWftwjTpWjk32GE qRhTx6enlS7tDov1h2AwwSkblz82h8JgZB+aVWMLIAv1Xnk9u4hZy6DIrE14005A0PjZRqkPuB2fd 9pQJ31sVkRFu3pk2X2CoLLhTBfS6L2eC/pdvmB7cMPhS2pSvCIPFV0IWmzn/48F4Di46fBwX5l0xG VwynFznkR+Ileik6MJ7oS6Z+MzkwTc5j/DVZYEkO/mi5yYHFcdEcibiQOQl7g5LDfzjwOYHBxU6J2 Ac71y7asHOY/dyznBs4vHBlyJo4OjHq0vDkSc2Pbl6eB099URbyNcCnoFq7TyvPoTmpWw27vopq4R 5wMNYHCAA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jyPDZ-0004AW-Kt; Thu, 23 Jul 2020 00:36:13 +0000 Received: from mail29.static.mailgun.info ([104.130.122.29]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jyPDR-00047m-Be for linux-arm-kernel@lists.infradead.org; Thu, 23 Jul 2020 00:36:11 +0000 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1595464570; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=S0uQeVpyP78JvbH1JlpQXM/q+1jpZi2huSddLdNND7s=; b=IHz98g6hI/UEYVl1XVzn4OlILLqGef3mF8EYeeWw4eKRjhwJ0tLQDA2PpjaZtW7eXkf0SEc3 STiYWo30nBa1VvE+LARoa7jNJNtgYZwyRhlh3UJ3U1prjnhuvwQP25KATriwXibqcWxkXOqU 7RYMHMVlRvJk2+eR5SxBcQVPxhw= X-Mailgun-Sending-Ip: 104.130.122.29 X-Mailgun-Sid: WyJiYzAxZiIsICJsaW51eC1hcm0ta2VybmVsQGxpc3RzLmluZnJhZGVhZC5vcmciLCAiYmU5ZTRhIl0= 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 5f18db465b75bcda60e95a63 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Thu, 23 Jul 2020 00:35:18 GMT Received: by smtp.codeaurora.org (Postfix, from userid 1001) id D9978C4339C; Thu, 23 Jul 2020 00:35:17 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: tingwei) by smtp.codeaurora.org (Postfix) with ESMTPSA id BC4C9C4339C; Thu, 23 Jul 2020 00:35:16 +0000 (UTC) MIME-Version: 1.0 Date: Thu, 23 Jul 2020 08:35:16 +0800 From: tingwei@codeaurora.org To: Greg KH Subject: Re: [PATCH v3 19/20] coresight: add try_get_module() in coresight_grab_device() In-Reply-To: <20200722104859.GA2827860@kroah.com> References: <20200717054536.7052-1-tingwei@codeaurora.org> <20200717054536.7052-20-tingwei@codeaurora.org> <7ef8d427-23c9-10cd-b337-03ae75476a8c@arm.com> <20200722104859.GA2827860@kroah.com> Message-ID: <49d35dc8429226e27d7638906cbc03ca@codeaurora.org> X-Sender: tingwei@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200722_203610_483458_4C10E5C0 X-CRM114-Status: GOOD ( 21.67 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: tsoni@codeaurora.org, saiprakash.ranjan@codeaurora.org, kim.phillips@arm.com, mathieu.poirier@linaro.org, Suzuki K Poulose , alexander.shishkin@linux.intel.com, coresight@lists.linaro.org, rdunlap@infradead.org, ykaukab@suse.de, linux@armlinux.org.uk, jinlmao@codeaurora.org, leo.yan@linaro.org, linux-arm-kernel , linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-07-22 18:48, Greg KH wrote: > On Wed, Jul 22, 2020 at 11:49:48AM +0100, Suzuki K Poulose wrote: >> Hi Tingwei, >> >> On 07/17/2020 06:45 AM, Tingwei Zhang wrote: >> > When coresight device is in an active session, driver module of >> > that device should not be removed. Use try_get_module() in >> > coresight_grab_device() to prevent module to be unloaded. >> > >> >> Is this really sufficient ? AFAIU, a device could be removed, but the >> module may still be alive due to the refcount on the module. This >> could imply that we have stale pointers in the _path_, which could >> lead to corruption elsewhere. Should we do a get/put_device() instead >> ? > > Remember there are two separate things here, code and data. There are > two different reference counts for them, do not confuse the two. > > get/put is needed when you have a reference to the data, module stuff > is > when you are calling into code. > > But note that you do not always need to grab a reference count to the > module, as long as the module can properly tear the data down when it > is > asked to be removed. Look at networking drivers as a great example of > that. > > thanks, > > greg k-h > Hi Greg, Understand your point. I made the attempt to not hold the refcount of module but stop/clean up active session in v1 of this series. Link is as below. https://lore.kernel.org/linux-arm-kernel/20200701071427.10477-1-tingwei@codeaurora.org/ However, there's a lot of tricks to play to make it work especially on perf trace when trace session is dynamically created/start/stop by perf framework. It may have performance overhead as well. With the suggestion from Mathieu, I'm wondering whether this complexity introduced really worth. Remove a coresight module driver with active trace session ongoing is a corner case. From v2, I turned to another alternative to grad a reference count to module when the operation function in that module could be called by coresight framework. That's a simpler and cleaner solution in my opinion. Thanks, Tingwei > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel