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Shutemov" , Jan Kara , stable References: <20210611161545.998858-1-jannh@google.com> <20210611153624.65badf761078f86f76365ab9@linux-foundation.org> From: John Hubbard Message-ID: <9041f85d-515d-576d-21a9-6f10b6e1279e@nvidia.com> Date: Sat, 12 Jun 2021 00:17:05 -1000 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [172.20.187.6] X-ClientProxiedBy: HQMAIL105.nvidia.com (172.20.187.12) To HQMAIL107.nvidia.com (172.20.187.13) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: f3603c15-1a72-4468-0d06-08d92d8b3c3b X-MS-TrafficTypeDiagnostic: BYAPR12MB2997: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:4303; X-MS-Exchange-SenderADCheck: 1 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:216.228.112.34;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:schybrid03.nvidia.com;CAT:NONE;SFS:(4636009)(396003)(346002)(136003)(376002)(39860400002)(46966006)(36840700001)(186003)(336012)(82310400003)(7636003)(31686004)(82740400003)(356005)(36860700001)(2906002)(110136005)(36756003)(53546011)(8676002)(54906003)(4326008)(31696002)(86362001)(7696005)(83380400001)(316002)(36906005)(47076005)(70586007)(16526019)(26005)(70206006)(8936002)(2616005)(426003)(5660300002)(478600001)(14583001)(43740500002);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Jun 2021 10:17:08.2823 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: f3603c15-1a72-4468-0d06-08d92d8b3c3b X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.34];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CO1NAM11FT059.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR12MB2997 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 5364FE000255 Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=Nvidia.com header.s=selector2 header.b=sGagCNB9; spf=none (imf30.hostedemail.com: domain of jhubbard@nvidia.com has no SPF policy when checking 40.107.94.64) smtp.mailfrom=jhubbard@nvidia.com; dmarc=pass (policy=none) header.from=nvidia.com X-Stat-Signature: 7c49dqjesxz1nj5zhouq8ue5rmbj53fk X-HE-Tag: 1623493027-5122 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 6/11/21 3:49 PM, Jann Horn wrote: > On Sat, Jun 12, 2021 at 12:36 AM Andrew Morton > wrote: >> On Fri, 11 Jun 2021 18:15:45 +0200 Jann Horn wrote: >>> +/* Equivalent to calling put_page() @refs times. */ >>> +static void put_page_refs(struct page *page, int refs) >>> +{ >>> + VM_BUG_ON_PAGE(page_ref_count(page) < refs, page); >> >> I don't think there's a need to nuke the whole kernel in this case. >> Can we warn then simply leak the page? That way we have a much better >> chance of getting a good bug report. > > Ah, yeah, I guess that makes sense. I had just copied this over from > put_compound_head(), and figured it was fine to keep it as-is, but I > guess changing it would be reasonable. I'm not quite sure what the > best way to do that would be though. > > I guess the check should go away in !DEBUG_VM builds? > > Should I just explicitly put the check in an ifdef block? Like so: > > #ifdef CONFIG_DEBUG_VM > if (VM_WARN_ON_ONCE_PAGE(...)) > return; > #endif > > Or, since inline ifdeffery looks ugly, get rid of the explicit ifdef, Agreed: VM_WARN_ON_ONCE_PAGE(), at least at the API level, seems like the best thing to use here. However, as you point out below, it needs a little something first. > and change the !DEBUG_VM definition of VM_WARN_ON_ONCE_PAGE() as > follows so that the branch is compiled away? > > #define VM_WARN_ON_ONCE_PAGE(cond, page) (BUILD_BUG_ON_INVALID(cond), false) > > That would look kinda neat, but it would be different from the > behavior of WARN_ON(), which still returns the original condition even > in !BUG builds, so that could be confusing... > The VM_WARN_ON_ONCE_PAGE() is not implemented exactly right in the !CONFIG_DEBUG_VM case. IMHO it should follow the WARN*() behavior, and return the original condition and keep going in that case. Then you could use it directly here. thanks, -- John Hubbard NVIDIA