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Wed, 25 Mar 2020 12:14:10 +0000 Date: Wed, 25 Mar 2020 09:14:07 -0300 From: Jason Gunthorpe To: Michal Hocko Cc: linux-mm@kvack.org, =?utf-8?B?SsOpcsO0bWU=?= Glisse , Christoph Hellwig Subject: Re: [PATCH v3] mm/mmu_notifier: prevent unpaired invalidate_start and invalidate_end Message-ID: <20200325121407.GU13183@mellanox.com> References: <20200211205252.GA10003@ziepe.ca> <20200228135006.GA30885@ziepe.ca> <20200324194137.GQ13183@mellanox.com> <20200325080117.GY19542@dhcp22.suse.cz> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200325080117.GY19542@dhcp22.suse.cz> User-Agent: Mutt/1.9.4 (2018-02-28) X-ClientProxiedBy: MN2PR19CA0037.namprd19.prod.outlook.com (2603:10b6:208:19b::14) To VI1PR05MB4141.eurprd05.prod.outlook.com (2603:10a6:803:44::15) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from mlx.ziepe.ca (142.68.57.212) by MN2PR19CA0037.namprd19.prod.outlook.com (2603:10b6:208:19b::14) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2835.21 via Frontend Transport; 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If there are > > no comments I will go ahead to send it in the hmm PR. > > I will not block this but it still looks like a wrong approach. A more > robust solution would be to allow calling invalidate_range_end even for > the failing invalidate_start. That requires reliably walking a rcu list backwards under rcu. I don't have a good feeling about that algorithm. Do you know of a solution? Since we don't actually have any users that care about this any more, I felt this testable solution was better. Jason