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, 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 A1341C433DF for ; Wed, 29 Jul 2020 11:21:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 84EBD207FC for ; Wed, 29 Jul 2020 11:21:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726772AbgG2LVX convert rfc822-to-8bit (ORCPT ); Wed, 29 Jul 2020 07:21:23 -0400 Received: from szxga03-in.huawei.com ([45.249.212.189]:2998 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726365AbgG2LVV (ORCPT ); Wed, 29 Jul 2020 07:21:21 -0400 Received: from dggemi406-hub.china.huawei.com (unknown [172.30.72.56]) by Forcepoint Email with ESMTP id E3A8BB8278ABC432252B; Wed, 29 Jul 2020 19:21:19 +0800 (CST) Received: from DGGEMI424-HUB.china.huawei.com (10.1.199.153) by dggemi406-hub.china.huawei.com (10.3.17.144) with Microsoft SMTP Server (TLS) id 14.3.487.0; Wed, 29 Jul 2020 19:21:19 +0800 Received: from DGGEMI525-MBS.china.huawei.com ([169.254.6.120]) by DGGEMI424-HUB.china.huawei.com ([10.1.199.153]) with mapi id 14.03.0487.000; Wed, 29 Jul 2020 19:21:10 +0800 From: "Song Bao Hua (Barry Song)" To: Christoph Hellwig CC: "m.szyprowski@samsung.com" , "robin.murphy@arm.com" , "will@kernel.org" , "ganapatrao.kulkarni@cavium.com" , "catalin.marinas@arm.com" , "iommu@lists.linux-foundation.org" , Linuxarm , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "Zengtao (B)" , huangdaode , Jonathan Cameron , Nicolas Saenz Julienne , Steve Capper , Andrew Morton , Mike Rapoport Subject: RE: [PATCH v4 1/2] dma-direct: provide the ability to reserve per-numa CMA Thread-Topic: [PATCH v4 1/2] dma-direct: provide the ability to reserve per-numa CMA Thread-Index: AQHWYPN0xh/nM4EZ4kKvOhwzWqp/oakcYyKAgACGKwD//4JGAIACAmig Date: Wed, 29 Jul 2020 11:21:09 +0000 Message-ID: References: <20200723131344.41472-1-song.bao.hua@hisilicon.com> <20200723131344.41472-2-song.bao.hua@hisilicon.com> <20200728115231.GA793@lst.de> <20200728122244.GA3639@lst.de> In-Reply-To: <20200728122244.GA3639@lst.de> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.126.203.121] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: Christoph Hellwig [mailto:hch@lst.de] > Sent: Wednesday, July 29, 2020 12:23 AM > To: Song Bao Hua (Barry Song) > Cc: Christoph Hellwig ; m.szyprowski@samsung.com; > robin.murphy@arm.com; will@kernel.org; ganapatrao.kulkarni@cavium.com; > catalin.marinas@arm.com; iommu@lists.linux-foundation.org; Linuxarm > ; linux-arm-kernel@lists.infradead.org; > linux-kernel@vger.kernel.org; Zengtao (B) ; > huangdaode ; Jonathan Cameron > ; Nicolas Saenz Julienne > ; Steve Capper ; Andrew > Morton ; Mike Rapoport > Subject: Re: [PATCH v4 1/2] dma-direct: provide the ability to reserve > per-numa CMA > > On Tue, Jul 28, 2020 at 12:19:03PM +0000, Song Bao Hua (Barry Song) wrote: > > I am sorry I haven't got your point yet. Do you mean something like the > below? > > > > arch/arm64/Kconfig: > > config CMDLINE > > string "Default kernel command string" > > - default "" > > + default "pernuma_cma=16M" > > help > > Provide a set of default command-line options at build time by > > entering them here. As a minimum, you should specify the the > > root device (e.g. root=/dev/nfs). > > Yes. > > > A background of the current code is that Linux distributions can usually use > arch/arm64/configs/defconfig > > directly to build kernel. cmdline can be easily ignored during the generation > of Linux distributions. > > I've not actually heard of a distro shipping defconfig yet.. > > > > > > if a way to expose this in the device tree might be useful, but people > > > more familiar with the device tree and the arm code will have to chime > > > in on that. > > > > Not sure if it is an useful user case as we are using ACPI but not device tree > since it is an ARM64 > > server with NUMA. > > Well, than maybe ACPI experts need to chime in on this. > > > > This seems to have lost the dma_contiguous_default_area NULL check. > > > > cma_alloc() is doing the check by returning NULL if cma is NULL. > > > > struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align, > > bool no_warn) > > { > > ... > > if (!cma || !cma->count) > > return NULL; > > } > > > > But I agree here the code can check before calling cma_alloc_aligned. > > Oh, indeed. Please split the removal of the NULL check in to a prep > patch then. Do you mean removing the NULL check in cma_alloc()? If so, it seems lot of places need to be changed: struct page *dma_alloc_from_contiguous(struct device *dev, size_t count, unsigned int align, bool no_warn) { if (align > CONFIG_CMA_ALIGNMENT) align = CONFIG_CMA_ALIGNMENT; + code to check dev_get_cma_area(dev) is not NULL return cma_alloc(dev_get_cma_area(dev), count, align, no_warn); } bool dma_release_from_contiguous(struct device *dev, struct page *pages, int count) { + code to check dev_get_cma_area(dev) is not NULL return cma_release(dev_get_cma_area(dev), pages, count); } bool cma_release(struct cma *cma, const struct page *pages, unsigned int count) { unsigned long pfn; + do we need to remove this !cma too if we remove it in cma_alloc()? if (!cma || !pages) return false; ... } And some other places where cma_alloc() and cma_release() are called: arch/powerpc/kvm/book3s_hv_builtin.c drivers/dma-buf/heaps/cma_heap.c drivers/s390/char/vmcp.c drivers/staging/android/ion/ion_cma_heap.c mm/hugetlb.c it seems many code were written with the assumption that cma_alloc/release will check if cma is null so they don't check it before calling cma_alloc(). And I am not sure if kernel robot will report error like pointer reference before checking it if !cma is removed in cma_alloc(). Thanks Barry 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, 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 A92EBC433E0 for ; Wed, 29 Jul 2020 11:22:20 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) (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 767F420809 for ; Wed, 29 Jul 2020 11:22:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 767F420809 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=hisilicon.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 4BF0E87FD6; Wed, 29 Jul 2020 11:22:20 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id OKgOaCcFZJgC; Wed, 29 Jul 2020 11:22:17 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by whitealder.osuosl.org (Postfix) with ESMTP id 9577187F81; Wed, 29 Jul 2020 11:22:17 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 86BFBC0050; Wed, 29 Jul 2020 11:22:17 +0000 (UTC) Received: from fraxinus.osuosl.org (smtp4.osuosl.org [140.211.166.137]) by lists.linuxfoundation.org (Postfix) with ESMTP id 2B2B7C004D for ; Wed, 29 Jul 2020 11:22:16 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by fraxinus.osuosl.org (Postfix) with ESMTP id E79EA8587E for ; Wed, 29 Jul 2020 11:21:30 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from fraxinus.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id wyeDSGtYgn0D for ; Wed, 29 Jul 2020 11:21:29 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from huawei.com (szxga03-in.huawei.com [45.249.212.189]) by fraxinus.osuosl.org (Postfix) with ESMTPS id 3030885876 for ; Wed, 29 Jul 2020 11:21:29 +0000 (UTC) Received: from dggemi406-hub.china.huawei.com (unknown [172.30.72.56]) by Forcepoint Email with ESMTP id E3A8BB8278ABC432252B; Wed, 29 Jul 2020 19:21:19 +0800 (CST) Received: from DGGEMI424-HUB.china.huawei.com (10.1.199.153) by dggemi406-hub.china.huawei.com (10.3.17.144) with Microsoft SMTP Server (TLS) id 14.3.487.0; Wed, 29 Jul 2020 19:21:19 +0800 Received: from DGGEMI525-MBS.china.huawei.com ([169.254.6.120]) by DGGEMI424-HUB.china.huawei.com ([10.1.199.153]) with mapi id 14.03.0487.000; Wed, 29 Jul 2020 19:21:10 +0800 From: "Song Bao Hua (Barry Song)" To: Christoph Hellwig Subject: RE: [PATCH v4 1/2] dma-direct: provide the ability to reserve per-numa CMA Thread-Topic: [PATCH v4 1/2] dma-direct: provide the ability to reserve per-numa CMA Thread-Index: AQHWYPN0xh/nM4EZ4kKvOhwzWqp/oakcYyKAgACGKwD//4JGAIACAmig Date: Wed, 29 Jul 2020 11:21:09 +0000 Message-ID: References: <20200723131344.41472-1-song.bao.hua@hisilicon.com> <20200723131344.41472-2-song.bao.hua@hisilicon.com> <20200728115231.GA793@lst.de> <20200728122244.GA3639@lst.de> In-Reply-To: <20200728122244.GA3639@lst.de> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.126.203.121] MIME-Version: 1.0 X-CFilter-Loop: Reflected Cc: "catalin.marinas@arm.com" , Mike Rapoport , Steve Capper , "robin.murphy@arm.com" , Linuxarm , "linux-kernel@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "Zengtao \(B\)" , "ganapatrao.kulkarni@cavium.com" , Andrew Morton , huangdaode , "will@kernel.org" , "linux-arm-kernel@lists.infradead.org" X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" > -----Original Message----- > From: Christoph Hellwig [mailto:hch@lst.de] > Sent: Wednesday, July 29, 2020 12:23 AM > To: Song Bao Hua (Barry Song) > Cc: Christoph Hellwig ; m.szyprowski@samsung.com; > robin.murphy@arm.com; will@kernel.org; ganapatrao.kulkarni@cavium.com; > catalin.marinas@arm.com; iommu@lists.linux-foundation.org; Linuxarm > ; linux-arm-kernel@lists.infradead.org; > linux-kernel@vger.kernel.org; Zengtao (B) ; > huangdaode ; Jonathan Cameron > ; Nicolas Saenz Julienne > ; Steve Capper ; Andrew > Morton ; Mike Rapoport > Subject: Re: [PATCH v4 1/2] dma-direct: provide the ability to reserve > per-numa CMA > > On Tue, Jul 28, 2020 at 12:19:03PM +0000, Song Bao Hua (Barry Song) wrote: > > I am sorry I haven't got your point yet. Do you mean something like the > below? > > > > arch/arm64/Kconfig: > > config CMDLINE > > string "Default kernel command string" > > - default "" > > + default "pernuma_cma=16M" > > help > > Provide a set of default command-line options at build time by > > entering them here. As a minimum, you should specify the the > > root device (e.g. root=/dev/nfs). > > Yes. > > > A background of the current code is that Linux distributions can usually use > arch/arm64/configs/defconfig > > directly to build kernel. cmdline can be easily ignored during the generation > of Linux distributions. > > I've not actually heard of a distro shipping defconfig yet.. > > > > > > if a way to expose this in the device tree might be useful, but people > > > more familiar with the device tree and the arm code will have to chime > > > in on that. > > > > Not sure if it is an useful user case as we are using ACPI but not device tree > since it is an ARM64 > > server with NUMA. > > Well, than maybe ACPI experts need to chime in on this. > > > > This seems to have lost the dma_contiguous_default_area NULL check. > > > > cma_alloc() is doing the check by returning NULL if cma is NULL. > > > > struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align, > > bool no_warn) > > { > > ... > > if (!cma || !cma->count) > > return NULL; > > } > > > > But I agree here the code can check before calling cma_alloc_aligned. > > Oh, indeed. Please split the removal of the NULL check in to a prep > patch then. Do you mean removing the NULL check in cma_alloc()? If so, it seems lot of places need to be changed: struct page *dma_alloc_from_contiguous(struct device *dev, size_t count, unsigned int align, bool no_warn) { if (align > CONFIG_CMA_ALIGNMENT) align = CONFIG_CMA_ALIGNMENT; + code to check dev_get_cma_area(dev) is not NULL return cma_alloc(dev_get_cma_area(dev), count, align, no_warn); } bool dma_release_from_contiguous(struct device *dev, struct page *pages, int count) { + code to check dev_get_cma_area(dev) is not NULL return cma_release(dev_get_cma_area(dev), pages, count); } bool cma_release(struct cma *cma, const struct page *pages, unsigned int count) { unsigned long pfn; + do we need to remove this !cma too if we remove it in cma_alloc()? if (!cma || !pages) return false; ... } And some other places where cma_alloc() and cma_release() are called: arch/powerpc/kvm/book3s_hv_builtin.c drivers/dma-buf/heaps/cma_heap.c drivers/s390/char/vmcp.c drivers/staging/android/ion/ion_cma_heap.c mm/hugetlb.c it seems many code were written with the assumption that cma_alloc/release will check if cma is null so they don't check it before calling cma_alloc(). And I am not sure if kernel robot will report error like pointer reference before checking it if !cma is removed in cma_alloc(). Thanks Barry _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu 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 431DAC433E0 for ; Wed, 29 Jul 2020 11:23:51 +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 0EE82207FC for ; Wed, 29 Jul 2020 11:23:51 +0000 (UTC) Authentication-Results: mail.kernel.org; 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Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k0k9J-0001J4-Vc; Wed, 29 Jul 2020 11:21:30 +0000 Received: from szxga03-in.huawei.com ([45.249.212.189] helo=huawei.com) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1k0k9H-0001IC-7H for linux-arm-kernel@lists.infradead.org; Wed, 29 Jul 2020 11:21:28 +0000 Received: from dggemi406-hub.china.huawei.com (unknown [172.30.72.56]) by Forcepoint Email with ESMTP id E3A8BB8278ABC432252B; Wed, 29 Jul 2020 19:21:19 +0800 (CST) Received: from DGGEMI424-HUB.china.huawei.com (10.1.199.153) by dggemi406-hub.china.huawei.com (10.3.17.144) with Microsoft SMTP Server (TLS) id 14.3.487.0; Wed, 29 Jul 2020 19:21:19 +0800 Received: from DGGEMI525-MBS.china.huawei.com ([169.254.6.120]) by DGGEMI424-HUB.china.huawei.com ([10.1.199.153]) with mapi id 14.03.0487.000; Wed, 29 Jul 2020 19:21:10 +0800 From: "Song Bao Hua (Barry Song)" To: Christoph Hellwig Subject: RE: [PATCH v4 1/2] dma-direct: provide the ability to reserve per-numa CMA Thread-Topic: [PATCH v4 1/2] dma-direct: provide the ability to reserve per-numa CMA Thread-Index: AQHWYPN0xh/nM4EZ4kKvOhwzWqp/oakcYyKAgACGKwD//4JGAIACAmig Date: Wed, 29 Jul 2020 11:21:09 +0000 Message-ID: References: <20200723131344.41472-1-song.bao.hua@hisilicon.com> <20200723131344.41472-2-song.bao.hua@hisilicon.com> <20200728115231.GA793@lst.de> <20200728122244.GA3639@lst.de> In-Reply-To: <20200728122244.GA3639@lst.de> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.126.203.121] MIME-Version: 1.0 X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200729_072127_576215_3FD94053 X-CRM114-Status: GOOD ( 28.74 ) 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: "catalin.marinas@arm.com" , Mike Rapoport , Steve Capper , "robin.murphy@arm.com" , Jonathan Cameron , Linuxarm , "linux-kernel@vger.kernel.org" , "iommu@lists.linux-foundation.org" , Nicolas Saenz Julienne , "Zengtao \(B\)" , "ganapatrao.kulkarni@cavium.com" , Andrew Morton , huangdaode , "will@kernel.org" , "linux-arm-kernel@lists.infradead.org" , "m.szyprowski@samsung.com" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org > -----Original Message----- > From: Christoph Hellwig [mailto:hch@lst.de] > Sent: Wednesday, July 29, 2020 12:23 AM > To: Song Bao Hua (Barry Song) > Cc: Christoph Hellwig ; m.szyprowski@samsung.com; > robin.murphy@arm.com; will@kernel.org; ganapatrao.kulkarni@cavium.com; > catalin.marinas@arm.com; iommu@lists.linux-foundation.org; Linuxarm > ; linux-arm-kernel@lists.infradead.org; > linux-kernel@vger.kernel.org; Zengtao (B) ; > huangdaode ; Jonathan Cameron > ; Nicolas Saenz Julienne > ; Steve Capper ; Andrew > Morton ; Mike Rapoport > Subject: Re: [PATCH v4 1/2] dma-direct: provide the ability to reserve > per-numa CMA > > On Tue, Jul 28, 2020 at 12:19:03PM +0000, Song Bao Hua (Barry Song) wrote: > > I am sorry I haven't got your point yet. Do you mean something like the > below? > > > > arch/arm64/Kconfig: > > config CMDLINE > > string "Default kernel command string" > > - default "" > > + default "pernuma_cma=16M" > > help > > Provide a set of default command-line options at build time by > > entering them here. As a minimum, you should specify the the > > root device (e.g. root=/dev/nfs). > > Yes. > > > A background of the current code is that Linux distributions can usually use > arch/arm64/configs/defconfig > > directly to build kernel. cmdline can be easily ignored during the generation > of Linux distributions. > > I've not actually heard of a distro shipping defconfig yet.. > > > > > > if a way to expose this in the device tree might be useful, but people > > > more familiar with the device tree and the arm code will have to chime > > > in on that. > > > > Not sure if it is an useful user case as we are using ACPI but not device tree > since it is an ARM64 > > server with NUMA. > > Well, than maybe ACPI experts need to chime in on this. > > > > This seems to have lost the dma_contiguous_default_area NULL check. > > > > cma_alloc() is doing the check by returning NULL if cma is NULL. > > > > struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align, > > bool no_warn) > > { > > ... > > if (!cma || !cma->count) > > return NULL; > > } > > > > But I agree here the code can check before calling cma_alloc_aligned. > > Oh, indeed. Please split the removal of the NULL check in to a prep > patch then. Do you mean removing the NULL check in cma_alloc()? If so, it seems lot of places need to be changed: struct page *dma_alloc_from_contiguous(struct device *dev, size_t count, unsigned int align, bool no_warn) { if (align > CONFIG_CMA_ALIGNMENT) align = CONFIG_CMA_ALIGNMENT; + code to check dev_get_cma_area(dev) is not NULL return cma_alloc(dev_get_cma_area(dev), count, align, no_warn); } bool dma_release_from_contiguous(struct device *dev, struct page *pages, int count) { + code to check dev_get_cma_area(dev) is not NULL return cma_release(dev_get_cma_area(dev), pages, count); } bool cma_release(struct cma *cma, const struct page *pages, unsigned int count) { unsigned long pfn; + do we need to remove this !cma too if we remove it in cma_alloc()? if (!cma || !pages) return false; ... } And some other places where cma_alloc() and cma_release() are called: arch/powerpc/kvm/book3s_hv_builtin.c drivers/dma-buf/heaps/cma_heap.c drivers/s390/char/vmcp.c drivers/staging/android/ion/ion_cma_heap.c mm/hugetlb.c it seems many code were written with the assumption that cma_alloc/release will check if cma is null so they don't check it before calling cma_alloc(). And I am not sure if kernel robot will report error like pointer reference before checking it if !cma is removed in cma_alloc(). Thanks Barry _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel