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Fri, 9 Oct 2020 12:15:22 +0000 Subject: Re: [PATCH 1/4] mm: introduce vma_set_file function v2 To: Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linaro-mm-sig@lists.linaro.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, chris@chris-wilson.co.uk, airlied@redhat.com, akpm@linux-foundation.org, sumit.semwal@linaro.org References: <20201008112342.9394-1-christian.koenig@amd.com> <20201008141211.GG438822@phenom.ffwll.local> <8fc28dfa-4bae-bee1-5aca-4e3c6e88b994@gmail.com> <20201009073900.GL438822@phenom.ffwll.local> <20201009121220.GM5177@ziepe.ca> From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: Date: Fri, 9 Oct 2020 14:15:16 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 In-Reply-To: <20201009121220.GM5177@ziepe.ca> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Originating-IP: [2a02:908:1252:fb60:be8a:bd56:1f94:86e7] X-ClientProxiedBy: AM0PR08CA0024.eurprd08.prod.outlook.com (2603:10a6:208:d2::37) To MN2PR12MB3775.namprd12.prod.outlook.com (2603:10b6:208:159::19) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2a02:908:1252:fb60:be8a:bd56:1f94:86e7] (2a02:908:1252:fb60:be8a:bd56:1f94:86e7) by AM0PR08CA0024.eurprd08.prod.outlook.com (2603:10a6:208:d2::37) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3455.21 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: 1dfe88c0-0b3a-4929-cfcc-08d86c4cfec2 X-MS-Exchange-CrossTenant-AuthSource: MN2PR12MB3775.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Oct 2020 12:15:22.3807 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 0c3VChSHEZGkcxa28wQgdcF2P0EDXEwRHqhhfcU/yb6CSBZDCsIsYtNAmdbw6TiA X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL0PR12MB2545 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: Am 09.10.20 um 14:12 schrieb Jason Gunthorpe: > On Fri, Oct 09, 2020 at 09:39:00AM +0200, Daniel Vetter wrote: >> I just noticed this here in the patch because everyone else does not do >> this. But looking at the mmap_region() code in mmap.c we seem to indeed >> have this problem for the error path: >> >> unmap_and_free_vma: >> vma->vm_file = NULL; >> fput(file); >> >> Note that the success path does things correctly (a bit above): >> >> file = vma->vm_file; >> out: >> >> So it indeed looks like dma-buf is the only one that does this fully >> correctly. So maybe we should do a follow-up patch to change the >> mmap_region exit code to pick up whatever vma->vm_file was set instead, >> and fput that? > Given that this new vma_set_file() should be the only way to > manipulate vm_file from the mmap op, I think this reflects a bug in > mm/mmap.c.. Should be: > > unmap_and_free_vma: > fput(vma->vm_file); > vma->vm_file = NULL; > > Then everything works the way you'd expect without tricky error > handling That's what Daniel suggested as well, yes. Going to craft a separate patch for this. Thanks, Christian. > > Jason