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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.1 Subject: Re: [PATCH v2 10/10] mm/hugetlb: Document why page_vma_mapped_walk() is safe to walk Content-Language: en-US To: Peter Xu , , CC: Jann Horn , Andrea Arcangeli , James Houghton , Rik van Riel , Miaohe Lin , Nadav Amit , "Mike Kravetz" , David Hildenbrand , Andrew Morton , Muchun Song References: <20221207203034.650899-1-peterx@redhat.com> <20221207203158.651092-1-peterx@redhat.com> From: John Hubbard In-Reply-To: <20221207203158.651092-1-peterx@redhat.com> 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: BL02EPF00010206:EE_|BL1PR12MB5031:EE_ X-MS-Office365-Filtering-Correlation-Id: eb71f8d4-94c0-4263-3106-08dad8b171fb X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Dec 2022 00:16:25.7257 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: eb71f8d4-94c0-4263-3106-08dad8b171fb 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: BL02EPF00010206.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL1PR12MB5031 X-Rspamd-Queue-Id: 5CF2740016 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: x5tx7b3uyr4495ft93dkcyzm43mymzeu X-HE-Tag: 1670458589-100389 X-HE-Meta: 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 UWZoz83G Wk88rr3Cpk/B4eiKLIgH+BQJcZPRLgMGhIaCXJSJzHIMBJBNa6UA3tTqso7x4Q1FbxozxshPjFzbQnLXhymLAnqwbHwI26STR2m1b 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 12/7/22 12:31, Peter Xu wrote: > Taking vma lock here is not needed for now because all potential hugetlb > walkers here should have i_mmap_rwsem held. Document the fact. > > Reviewed-by: Mike Kravetz > Signed-off-by: Peter Xu > --- > mm/page_vma_mapped.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > index e97b2e23bd28..2e59a0419d22 100644 > --- a/mm/page_vma_mapped.c > +++ b/mm/page_vma_mapped.c > @@ -168,8 +168,14 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > /* The only possible mapping was handled on last iteration */ > if (pvmw->pte) > return not_found(pvmw); > - > - /* when pud is not present, pte will be NULL */ > + /* > + * NOTE: we don't need explicit lock here to walk the > + * hugetlb pgtable because either (1) potential callers of > + * hugetlb pvmw currently holds i_mmap_rwsem, or (2) the > + * caller will not walk a hugetlb vma (e.g. ksm or uprobe). > + * When one day this rule breaks, one will get a warning > + * in hugetlb_walk(), and then we'll figure out what to do. > + */ Confused. Is this documentation actually intended to refer to hugetlb_walk() itself, or just this call site? If the former, then let's move it over to be right before hugetlb_walk(). > pvmw->pte = hugetlb_walk(vma, pvmw->address, size); > if (!pvmw->pte) > return false; thanks, -- John Hubbard NVIDIA