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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4CA6CC25B08 for ; Wed, 17 Aug 2022 05:36:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232048AbiHQFgt (ORCPT ); Wed, 17 Aug 2022 01:36:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54318 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238334AbiHQFgd (ORCPT ); Wed, 17 Aug 2022 01:36:33 -0400 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 92C3D65560 for ; Tue, 16 Aug 2022 22:36:32 -0700 (PDT) Received: by verein.lst.de (Postfix, from userid 2407) id 8176D68AA6; Wed, 17 Aug 2022 07:36:28 +0200 (CEST) Date: Wed, 17 Aug 2022 07:36:28 +0200 From: Christoph Hellwig To: Robin Murphy Cc: Marek Szyprowski , Liu Song , akpm@linux-foundation.org, "linux-arm-kernel@lists.infradead.org" , Christoph Hellwig , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "iommu@lists.linux.dev" Subject: Re: [PATCH v2] mm/dmapool.c: avoid duplicate memset within dma_pool_alloc Message-ID: <20220817053628.GA28747@lst.de> References: <1658125690-76930-1-git-send-email-liusong@linux.alibaba.com> <1dbe63ff-5575-745b-653a-a992ae53e1aa@samsung.com> <413d8666-7a82-efd7-6716-13658016ca10@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <413d8666-7a82-efd7-6716-13658016ca10@arm.com> User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>> A helper function "use_dev_coherent_memory" is introduced here to >>> determine whether the memory is allocated by "dma_alloc_from_dev_coherent". >>> >>> And use "get_dma_ops" to determine whether the memory is allocated by >>> "dma_direct_alloc". WTF? get_dma_ops is privat to the DMA API layer, and dmapool has no business even using that. Even independent of this particular case, consumers of an API never have any business looking at the implementation of the API, that is the whole point of the abstraction. > It's not even that, the change here is just obviously broken, since it ends > up entirely ignoring want_init_on_alloc() for devices using dma-direct. > Sure, the memory backing a dma_page is zeroed *once* by its initial > dma-coherent allocation, but who says we're not not reallocating pool > entries from an existing dma_page? And yes, in addition to that it also is completely broken.