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Mercier" , syzbot+5d4cb6b4409edfd18646@syzkaller.appspotmail.com, linux-fsdevel@vger.kernel.org, Zhiguo Jiang , Sumit Semwal , linux-media@vger.kernel.org References: <20240423191310.19437-1-dmantipov@yandex.ru> <85b476cd-3afd-4781-9168-ecc88b6cc837@amd.com> <3a7d0f38-13b9-4e98-a5fa-9a0d775bcf81@yandex.ru> <72f5f1b8-ca5b-4207-9ac9-95b60c607f3a@amd.com> <5c8345ee-011a-4fa7-8326-84f40daf2f2c@yandex.ru> <20240506-6128db77520dbf887927bd4d-pchelkin@ispras.ru> Content-Language: en-US From: =?UTF-8?Q?Christian_K=C3=B6nig?= In-Reply-To: <20240506-6128db77520dbf887927bd4d-pchelkin@ispras.ru> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: FR0P281CA0249.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:af::15) To PH7PR12MB5685.namprd12.prod.outlook.com (2603:10b6:510:13c::22) Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH7PR12MB5685:EE_|LV3PR12MB9267:EE_ X-MS-Office365-Filtering-Correlation-Id: be4a6ec2-1f6c-4d2f-acab-08dc6e7c44f5 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230031|7416005|376005|1800799015|366007; 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May 14:08, Dmitry Antipov wrote: >> On 5/3/24 11:18 AM, Christian König wrote: >> >>> Attached is a compile only tested patch, please verify if it fixes your problem. >> LGTM, and this is similar to get_file() in __pollwait() and fput() in >> free_poll_entry() used in implementation of poll(). Please resubmit to >> linux-fsdevel@ including the following: >> >> Reported-by: syzbot+5d4cb6b4409edfd18646@syzkaller.appspotmail.com >> Closes: https://syzkaller.appspot.com/bug?extid=5d4cb6b4409edfd18646 >> Tested-by: Dmitry Antipov > I guess the problem is addressed by commit 4efaa5acf0a1 ("epoll: be better > about file lifetimes") which was pushed upstream just before v6.9-rc7. > > Link: https://lore.kernel.org/lkml/0000000000002d631f0615918f1e@google.com/ Yeah, Linus took care of that after convincing Al that this is really a bug. They key missing information was that we have a mutex which makes sure that fput() blocks for epoll to stop the polling. It also means that you should probably re-consider using epoll together with shared DMA-bufs. Background is that when both client and display server try to use epoll the kernel will return an error because there can only be one user of epoll. Regards, Christian.