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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH v2 05/10] mm/hugetlb: Make userfaultfd_huge_must_wait() safe to pmd unshare Content-Language: en-US To: Peter Xu CC: , , Muchun Song , Andrea Arcangeli , "James Houghton" , Jann Horn , Rik van Riel , Miaohe Lin , Andrew Morton , Mike Kravetz , "David Hildenbrand" , Nadav Amit References: <20221207203034.650899-1-peterx@redhat.com> <20221207203034.650899-6-peterx@redhat.com> From: John Hubbard In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.126.231.37] X-ClientProxiedBy: rnnvmail203.nvidia.com (10.129.68.9) To rnnvmail201.nvidia.com (10.129.68.8) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN8NAM11FT078:EE_|SA0PR12MB4559:EE_ X-MS-Office365-Filtering-Correlation-Id: 70f51bda-23e4-45bf-17df-08dad8ae6bc9 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:216.228.117.161;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge2.nvidia.com;CAT:NONE;SFS:(13230022)(4636009)(346002)(136003)(376002)(39860400002)(396003)(451199015)(36840700001)(40470700004)(46966006)(8936002)(336012)(5660300002)(4744005)(31686004)(31696002)(426003)(86362001)(47076005)(7416002)(478600001)(36860700001)(40460700003)(40480700001)(16576012)(83380400001)(4326008)(82310400005)(186003)(41300700001)(16526019)(82740400003)(70586007)(70206006)(2906002)(26005)(2616005)(7636003)(356005)(8676002)(53546011)(6916009)(316002)(54906003)(36756003)(14583001)(43740500002);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Dec 2022 23:54:46.8565 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 70f51bda-23e4-45bf-17df-08dad8ae6bc9 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT078.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA0PR12MB4559 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/7/22 15:44, Peter Xu wrote: > The part that matters in the comment is "need to be before setting current > state". > > blocking_state = userfaultfd_get_blocking_state(vmf->flags); > if (is_vm_hugetlb_page(vma)) > hugetlb_vma_lock_read(vma); > set_current_state(blocking_state); > > down_read() can sleep and also modify the task state, we cannot take the > lock after that point because otherwise the task state will be messed up. > OK, how about: /* * Take the vma lock now, in order to safely call * userfaultfd_huge_must_wait() a little bit later. Because acquiring * the (sleepable) vma lock potentially modifies the current task state, * that must be before explicitly calling set_current_state(). */ Other than that, the patch looks good, so: Reviewed-by: John Hubbard thanks, -- John Hubbard NVIDIA