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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.2 Subject: Re: [PATCH] [suggestion] mm/gup: avoid IS_ERR_OR_NULL To: Jason Gunthorpe , Lorenzo Stoakes CC: Arnd Bergmann , Andrew Morton , Arnd Bergmann , Catalin Marinas , Will Deacon , Peter Zijlstra , Ingo Molnar , "Arnaldo Carvalho de Melo" , Mark Rutland , "Alexander Shishkin" , Jiri Olsa , Namhyung Kim , Ian Rogers , "Adrian Hunter" , , , , References: <20230519093953.10972-1-arnd@kernel.org> <5b071f65-7f87-4a7b-a76a-f4a1c1568ae7@lucifer.local> <1ca47b8a-292c-47ab-aa6f-ca24fdfc0d3c@lucifer.local> <0bc9dc2b-0da6-4d5c-96af-e21aa287eecb@lucifer.local> <617c2e26-8450-4a35-9b47-c0482921f030@lucifer.local> Content-Language: en-US From: John Hubbard In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.126.230.35] 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: CO1NAM11FT035:EE_|SJ2PR12MB8691:EE_ X-MS-Office365-Filtering-Correlation-Id: 4e2d4b8f-556b-4c69-999c-08db5fd05764 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: 28 May 2023 23:07:42.5697 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 4e2d4b8f-556b-4c69-999c-08db5fd05764 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: CO1NAM11FT035.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ2PR12MB8691 X-Rspamd-Queue-Id: 8940914000A X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: kbx5dt37dghwu9jyb5966qqto8a5g3b3 X-HE-Tag: 1685315266-598982 X-HE-Meta: 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 RjChM6Qo b8mbJw+trH8UEE22u4pz7JxInEgBke6aCc4JLFsVJ+qKiiqEr3Cz65pmrg9R7sNrIFLW2F3z0eaYonnHCScGXd9CvS/0qrdXUapRoTS3Na+arRKGubtIst0OWXzscGQPdLZaRKaKhEjqp3vwITQBGNhx0wjJNw6Ez/5cpg+eMx+s8l5tTMejftRoDDRPMDJqHsVqjNNR/cbPVEo/yGV2lWxW+n8G7JQJ4F4S4DaOWhEA4OUuO+bQ3rsqrFDZ/TOQwhpdrI5iDVjcaL/1ijyvTnrD+IfktPnh85b2A/2PQMfnQ6OChNxNVpDn12gBo4+4nfFl8UzNaq4v3Pyg= 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 5/28/23 09:22, Jason Gunthorpe wrote: > On Sun, May 28, 2023 at 04:13:44PM +0100, Lorenzo Stoakes wrote: >> On Sat, May 27, 2023 at 06:52:01AM -0300, Jason Gunthorpe wrote: >>> On Sat, May 20, 2023 at 10:12:40AM +0100, Lorenzo Stoakes wrote: >>>>> No, this returning 0 on failure is a foot gun. Failing to pin a single >>>>> page is always an error, the only question is what sub reason caused >>>>> the error to happen. There is no third case where it is not an error. >>>> >>>> The uprobe path thinks otherwise, but maybe the answer is that we just need >>>> to -EFAULT on missing VMA and -EPERM on invalid flags. >>> >>> I think uprobe is just broken to think there is a third outcome. Let's >>> just fix it instead of trying to pretend it makes sense. >> >> Sure, will take a look at that if I get a chance. We can at the very least >> adjust get_user_page_vma_remote() with this fixed. Great! We've had previous discussions about getting rid of this pseudo-tristate errno in gup, so I just wanted to mention that I'm also glad to see the movement toward, "return some pages, or else a -errno". That's progress. >> >> Do you feel that a partially successful pinning for other GUP callers >> should equally be treated as an error (and pages unpinned -> return error >> code)? In that instance we'd need to audit things somewhat. > > That seems more deeply ingrained at least, I'm not as keen to change > it as to get rid of the 0 return result. > Yes. It's not just "audit things somewhat", it's more like, "change quite a few call sites, some of which actually gather sets of partial results in a retry loop". So some actual coding changes there. thanks, -- John Hubbard NVIDIA