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=-5.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 20C7FC433E0 for ; Wed, 22 Jul 2020 11:22:40 +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 DD14E20771 for ; Wed, 22 Jul 2020 11:22:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="lc/RCeVL" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DD14E20771 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com 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:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=gJC8m4HaZba+7kcKRGW1+IwVj1K15qh3S3nKo1InUgg=; b=lc/RCeVL+dU7lTDbNxqpJ+/E1 KjK5a8NSxjjknjwK49YfWkvzBKvfF31e+SyKtUZDCNfmpYHDNz9WRecJLchQOZzzooZpRgA9O+qnp BElpnZqLs3RZkcZj5ODrbCS3fe55I/pzsohIpqvx91G0z5y4n1laKY63m3ahw5Cil7Abjs0b2mJcG mUAaYpt6YrFxHXvipke3qfQbWtCiuLSiQ89dxR8axhPZyZjviMdMMKANN1sRE8u4AKShQPCkHdtac tKbHamkjVx1pCe8dPP34fnhSlXD7hLynRdygZwLa7x3KuYKchEqNfBCM+4CD6CglpDGdkZlecCp0o IwM3JUegA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jyCo7-00083h-0C; Wed, 22 Jul 2020 11:21:07 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jyCo4-00082x-5O for linux-arm-kernel@lists.infradead.org; Wed, 22 Jul 2020 11:21:05 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9BF0031B; Wed, 22 Jul 2020 04:21:01 -0700 (PDT) Received: from [10.37.12.71] (unknown [10.37.12.71]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C39213F66F; Wed, 22 Jul 2020 04:20:57 -0700 (PDT) Subject: Re: [PATCH v3 19/20] coresight: add try_get_module() in coresight_grab_device() To: gregkh@linuxfoundation.org References: <20200717054536.7052-1-tingwei@codeaurora.org> <20200717054536.7052-20-tingwei@codeaurora.org> <7ef8d427-23c9-10cd-b337-03ae75476a8c@arm.com> <20200722104859.GA2827860@kroah.com> From: Suzuki K Poulose Message-ID: Date: Wed, 22 Jul 2020 12:26:09 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20200722104859.GA2827860@kroah.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200722_072104_278903_A5338178 X-CRM114-Status: GOOD ( 22.04 ) 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, alexander.shishkin@linux.intel.com, coresight@lists.linaro.org, rdunlap@infradead.org, ykaukab@suse.de, linux@armlinux.org.uk, jinlmao@codeaurora.org, tingwei@codeaurora.org, leo.yan@linaro.org, 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 07/22/2020 11:48 AM, 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. Exactly. In this case, we have reference to the data specific to the device in a data structure specific to one session, which doesn't have any link back from the device to release it. Thus we need get/put here to make sure that data doesn't get released under our feet. > > 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 Suzuki _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel