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Shutemov" , Davidlohr Bueso , Prakash Sangappa , James Houghton , Mina Almasry , Pasha Tatashin , Axel Rasmussen , Ray Fucillo , Andrew Morton Subject: Re: [RFC PATCH v4 8/8] hugetlb: use new vma_lock for pmd sharing synchronization Message-ID: References: <20220706202347.95150-1-mike.kravetz@oracle.com> <20220706202347.95150-9-mike.kravetz@oracle.com> <2adbbbd2-51d2-744d-77b4-374fe651873b@huawei.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2adbbbd2-51d2-744d-77b4-374fe651873b@huawei.com> X-ClientProxiedBy: MW4PR04CA0032.namprd04.prod.outlook.com (2603:10b6:303:6a::7) To BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 290f3437-68a2-40ec-f63d-08da718991aa X-MS-TrafficTypeDiagnostic: CY4PR10MB1590:EE_ X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BY5PR10MB4196.namprd10.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230016)(7916004)(376002)(39860400002)(136003)(346002)(366004)(396003)(86362001)(44832011)(83380400001)(186003)(38100700002)(8936002)(5660300002)(7416002)(6486002)(316002)(66556008)(6916009)(478600001)(66476007)(33716001)(53546011)(6512007)(8676002)(54906003)(6506007)(9686003)(2906002)(41300700001)(6666004)(66946007)(26005)(4326008);DIR:OUT;SFP:1101; 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bh=/OKZN0+Ce+4f0fuHYVCwjEje+Bs1NOp2uhgQ8nvWnLk=; b=8OxQqzh+POJ6NeYygOKx+9szVJ3Fter50KwfNexuvMk+BDG+ZHJRBXgJBp/cG/KDP8xhPx itcnC9RJCNMHMtFldPETaEsOVkXeXzRxFaebZoxxHDvxlq/Xa7jLaoxAI54pp6k5HDTeEM AiPyondGIpgvf6Jimk4STDnUS+/Taa4= X-Rspamd-Queue-Id: 29147200B7 X-Rspam-User: X-Stat-Signature: 79zssxdnh4qbo69751ixuts8ryn3c3jt Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=oracle.com header.s=corp-2022-7-12 header.b=UyH+USuo; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b=jpFS3XPK; spf=pass (imf03.hostedemail.com: domain of mike.kravetz@oracle.com designates 205.220.177.32 as permitted sender) smtp.mailfrom=mike.kravetz@oracle.com; arc=pass ("microsoft.com:s=arcselector9901:i=1"); dmarc=pass (policy=none) header.from=oracle.com X-Rspamd-Server: rspam08 X-HE-Tag: 1659116504-937899 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 07/29/22 09:41, Miaohe Lin wrote: > On 2022/7/29 1:47, Mike Kravetz wrote: > > On 07/28/22 14:51, Miaohe Lin wrote: > snip > >> > >> Do we need to check &mm->mm_users == 0 here in case the address_space of corresponding process > >> has exited? In this case, mmdrop will drop the last reference and free the skipped_mm. So we will > >> use skipped_mm below after it's freed? > >> > > > > Good point! > > I think we need to wait to drop since we want to hold the read lock. > > Will update. > > > >>> + vma = find_vma(skipped_mm, skipped_vm_start); > >>> + if (!vma || vma->vm_file->f_mapping != mapping || > >> > >> If skipped_vm_start is unmapped and remapped as a anon vma before we taking the mmap_read_lock, > >> vma->vm_file will be NULL? > >> > > > > IIUC, vma->vm_file will always be set even for an anon vma. The fault > > code depends on this. See beginning of hugetlb_fault() where we > > unconditionally do: > > > > mapping = vma->vm_file->f_mapping; > > What if vma is non-hugetlb anon vma? > Right. The first check after !vma should be for hugetlb as we do not care if non-hugetlb vmas and want to quit. Something like, vma = find_vma(skipped_mm, skipped_vm_start); if (!vma || !is_vm_hugetlb_page(vma) || -- Mike Kravetz