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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 11D61C43387 for ; Thu, 10 Jan 2019 23:15:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D4C902173B for ; Thu, 10 Jan 2019 23:15:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728470AbfAJXPo (ORCPT ); Thu, 10 Jan 2019 18:15:44 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:40778 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728787AbfAJXPn (ORCPT ); Thu, 10 Jan 2019 18:15:43 -0500 Received: from pps.filterd (m0098417.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id x0AN91f8071751 for ; Thu, 10 Jan 2019 18:15:42 -0500 Received: from e11.ny.us.ibm.com (e11.ny.us.ibm.com [129.33.205.201]) by mx0a-001b2d01.pphosted.com with ESMTP id 2pxd32n8dm-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 10 Jan 2019 18:15:41 -0500 Received: from localhost by e11.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 10 Jan 2019 23:15:38 -0000 Received: from b01ledav004.gho.pok.ibm.com (b01ledav004.gho.pok.ibm.com [9.57.199.109]) by b01cxnp23034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x0ANFbHo20185194 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Thu, 10 Jan 2019 23:15:37 GMT Received: from b01ledav004.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 27F77112065; Thu, 10 Jan 2019 23:15:37 +0000 (GMT) Received: from b01ledav004.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3F1E7112064; Thu, 10 Jan 2019 23:15:36 +0000 (GMT) Received: from oc6857751186.ibm.com (unknown [9.85.156.211]) by b01ledav004.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 10 Jan 2019 23:15:36 +0000 (GMT) Subject: Re: [PATCH] ibmvscsi: use GFP_ATOMIC with dma_alloc_coherent in map_sg_data To: Christoph Hellwig Cc: james.bottomley@hansenpartnership.com, martin.petersen@oracle.com, linux-scsi@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, brking@linux.vnet.ibm.com, stable@vger.kernel.org References: <1547089136-20264-1-git-send-email-tyreld@linux.vnet.ibm.com> <20190110150703.GA26696@infradead.org> From: Tyrel Datwyler Date: Thu, 10 Jan 2019 15:15:35 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190110150703.GA26696@infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 19011023-2213-0000-0000-0000033A6ED5 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010381; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000274; SDB=6.01144652; UDB=6.00596015; IPR=6.00924917; MB=3.00025075; MTD=3.00000008; XFM=3.00000015; UTC=2019-01-10 23:15:40 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19011023-2214-0000-0000-00005CEBBE7B Message-Id: <4c5a470e-fa98-1ffd-7f55-5a4ffb3a692a@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-01-10_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=576 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1901100176 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On 01/10/2019 07:07 AM, Christoph Hellwig wrote: > On Wed, Jan 09, 2019 at 06:58:56PM -0800, Tyrel Datwyler wrote: >> While mapping DMA for scatter list when a scsi command is queued the >> existing call to dma_alloc_coherent() in our map_sg_data() function >> passes zero for the gfp_flags parameter. We are most definitly in atomic >> context at this point as queue_command() is called in softirq context >> and further we have a spinlock holding the scsi host lock. >> >> Fix this by passing GFP_ATOMIC to dma_alloc_coherent() to prevent any >> sort of sleeping in atomic context deadlock. > > This is a pretty clear sign you should not be using dma_alloc_coherent > to start with. GFP_ATOMIC support in many of the implementations either > doesn't work at all or is severly constrained. On a secondary note I was unaware of the GFP_ATOMIC limitations. Should this be added to the documentation somewhere? I don't see any mention here form DMA-API-HOWTO.txt. Using Consistent DMA mappings ============================= To allocate and map large (PAGE_SIZE or so) consistent DMA regions, you should do:: dma_addr_t dma_handle; cpu_addr = dma_alloc_coherent(dev, size, &dma_handle, gfp); where device is a ``struct device *``. This may be called in interrupt context with the GFP_ATOMIC flag. -Tyrel Given that the > descriptor is written by the OS and read by the hardware exactly once > there is no point in having the coherent mapping to start with. >