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=-0.8 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 3C968C433F5 for ; Thu, 6 Sep 2018 04:00:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E3D172083D for ; Thu, 6 Sep 2018 04:00:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E3D172083D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.ibm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727629AbeIFIdg (ORCPT ); Thu, 6 Sep 2018 04:33:36 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:36270 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725880AbeIFIdf (ORCPT ); Thu, 6 Sep 2018 04:33:35 -0400 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w863sdHV056213 for ; Thu, 6 Sep 2018 00:00:11 -0400 Received: from e32.co.us.ibm.com (e32.co.us.ibm.com [32.97.110.150]) by mx0b-001b2d01.pphosted.com with ESMTP id 2mavb3gvgw-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 06 Sep 2018 00:00:11 -0400 Received: from localhost by e32.co.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) Wed, 5 Sep 2018 22:00:07 -0600 Received: from b03ledav004.gho.boulder.ibm.com (b03ledav004.gho.boulder.ibm.com [9.17.130.235]) by b03cxnp07029.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w86406sC35061854 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 5 Sep 2018 21:00:06 -0700 Received: from b03ledav004.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id EA6097805C; Wed, 5 Sep 2018 22:00:05 -0600 (MDT) Received: from b03ledav004.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0D4B178064; Wed, 5 Sep 2018 22:00:03 -0600 (MDT) Received: from [9.102.0.183] (unknown [9.102.0.183]) by b03ledav004.gho.boulder.ibm.com (Postfix) with ESMTP; Wed, 5 Sep 2018 22:00:03 -0600 (MDT) Subject: Re: [RFC PATCH] mm/hugetlb: make hugetlb_lock irq safe To: Matthew Wilcox Cc: akpm@linux-foundation.org, Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20180905112341.21355-1-aneesh.kumar@linux.ibm.com> <20180905130440.GA3729@bombadil.infradead.org> <20180905134848.GB3729@bombadil.infradead.org> From: "Aneesh Kumar K.V" Date: Thu, 6 Sep 2018 09:30:02 +0530 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: <20180905134848.GB3729@bombadil.infradead.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 18090604-0004-0000-0000-00001484D2DF X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009676; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000266; SDB=6.01084192; UDB=6.00559575; IPR=6.00864192; MB=3.00023137; MTD=3.00000008; XFM=3.00000015; UTC=2018-09-06 04:00:08 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18090604-0005-0000-0000-000088B6DF5D Message-Id: <95b9a5d9-1e46-b969-4188-14c0a6efb215@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-09-06_01:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=481 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1809060041 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/05/2018 07:18 PM, Matthew Wilcox wrote: > On Wed, Sep 05, 2018 at 06:56:19PM +0530, Aneesh Kumar K.V wrote: >> On 09/05/2018 06:34 PM, Matthew Wilcox wrote: >>> On Wed, Sep 05, 2018 at 04:53:41PM +0530, Aneesh Kumar K.V wrote: >>>> inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. >>> >>> How do you go from "can be taken in softirq context" problem report to >>> "must disable hard interrupts" solution? Please explain why spin_lock_bh() >>> is not a sufficient fix. >>> >>>> swapper/68/0 [HC0[0]:SC1[1]:HE1:SE0] takes: >>>> 0000000052a030a7 (hugetlb_lock){+.?.}, at: free_huge_page+0x9c/0x340 >>>> {SOFTIRQ-ON-W} state was registered at: >>>> lock_acquire+0xd4/0x230 >>>> _raw_spin_lock+0x44/0x70 >>>> set_max_huge_pages+0x4c/0x360 >>>> hugetlb_sysctl_handler_common+0x108/0x160 >>>> proc_sys_call_handler+0x134/0x190 >>>> __vfs_write+0x3c/0x1f0 >>>> vfs_write+0xd8/0x220 >>> >>> Also, this only seems to trigger here. Is it possible we _already_ >>> have softirqs disabled through every other code path, and it's just this >>> one sysctl handler that needs to disable softirqs? Rather than every >>> lock access? >> >> Are you asking whether I looked at moving that put_page to a worker thread? > > No. I'm asking "why not disable softirqs in the sysctl handler". Or > perhaps equivalently, just replace spin_lock() with spin_lock_bh() in > set_max_huge_pages(). > Disabling only in sysctl handler is not enough right? Every usage of locks taken by the page destructor need to be converted to disable softirqs right? >> I didn't. The reason I looked at current patch is to enable the usage of >> put_page() from irq context. We do allow that for non hugetlb pages. So was >> not sure adding that additional restriction for hugetlb >> is really needed. Further the conversion to irqsave/irqrestore was >> straightforward. > > straightforward, sure. but is it the right thing to do? do we want to > be able to put_page() a hugetlb page from hardirq context? > -aneesh