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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 3ED21CA9EA1 for ; Fri, 18 Oct 2019 13:51:38 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (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 08305222C6 for ; Fri, 18 Oct 2019 13:51:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 08305222C6 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id BDA25B49; Fri, 18 Oct 2019 13:51:37 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 5E1BBB43 for ; Fri, 18 Oct 2019 13:51:36 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from foss.arm.com (unknown [217.140.110.172]) by smtp1.linuxfoundation.org (Postfix) with ESMTP id 105168AB for ; Fri, 18 Oct 2019 13:51:35 +0000 (UTC) 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 92E89FC2; Fri, 18 Oct 2019 06:51:27 -0700 (PDT) Received: from [10.1.197.57] (e110467-lin.cambridge.arm.com [10.1.197.57]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A52A03F6C4; Fri, 18 Oct 2019 06:51:26 -0700 (PDT) Subject: Re: [PATCH] iommu/dma: Relax locking in iommu_dma_prepare_msi() To: Christoph Hellwig References: <5af5e77102ca52576cb96816f0abcf6398820055.1571245656.git.robin.murphy@arm.com> <20191017162453.GA6012@infradead.org> From: Robin Murphy Message-ID: <2309c311-7378-385d-bf97-57965d36c18b@arm.com> Date: Fri, 18 Oct 2019 14:51:25 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20191017162453.GA6012@infradead.org> Content-Language: en-GB Cc: maz@kernel.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, julien.grall@arm.com X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org On 17/10/2019 17:24, Christoph Hellwig wrote: > On Wed, Oct 16, 2019 at 06:07:36PM +0100, Robin Murphy wrote: >> @@ -1180,7 +1179,7 @@ int iommu_dma_prepare_msi(struct msi_desc *desc, phys_addr_t msi_addr) >> struct iommu_domain *domain = iommu_get_domain_for_dev(dev); >> struct iommu_dma_cookie *cookie; >> struct iommu_dma_msi_page *msi_page; >> - unsigned long flags; >> + static DEFINE_MUTEX(msi_prepare_lock); > > Just a style nitpick, but I find locks declared inside functions > really weird. In addition to that locks not embedded into a structure > and not directly next to variables or data structures they protect > really need a comment explaining what they are trying to serialize. Hmm, the lock itself is merely a glorified comment, it's named for the operation it protects, its entire existence spans 15 consecutive lines, and 27% of those lines are dedicated to explaining that it's technically redundant. Is there *really* anything that isn't clear from the context? Robin. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu