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Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 Subject: Re: acm_port_shutdown hangs for 30 seconds Content-Language: en-US To: Jookia , linux-usb@vger.kernel.org References: From: Oliver Neukum In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR0P281CA0053.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:48::17) To VI1PR0401MB2526.eurprd04.prod.outlook.com (2603:10a6:800:58::16) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: f6babcdb-f1fa-4e76-eae0-08da59c7143e X-MS-TrafficTypeDiagnostic: VI1PR0402MB2735:EE_ X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:VI1PR0401MB2526.eurprd04.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230016)(366004)(396003)(376002)(136003)(39860400002)(346002)(2616005)(41300700001)(186003)(86362001)(36756003)(6486002)(31696002)(478600001)(66556008)(316002)(38100700002)(66476007)(8676002)(2906002)(66946007)(83380400001)(5660300002)(6512007)(31686004)(6506007)(53546011)(8936002)(43740500002)(45980500001);DIR:OUT;SFP:1101; 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Connect an Arduino Micro with stock LED blink firmware > 2. Run 'screen /dev/ttyACM1 9600' > 3. Type some letters (no response from the board is given) > 4. Quit in some way > > If I skip step 3 (typing letters), the hang does not happen. You have something in the buffer, which the tty layer will try to send. > In userspace the hang happens at a call to close() on the TTY, and using The tty layer is supposed to wait a defined amount of time if a tty needs to drain. This amount (among many other things) is traditionally set with the TIOCSSERIAL ioctl() > perf and ftrace it looks to be spending a lot of time poisoning urbs in > acm_port_shutdown. That is a bit odd. > - Is this a bug? Maybe, but unlikely. If and only it takes much more time than the termios say. > - Can I reduce the timeout somehow? ioctl() TIOCSSERIAL. If that does not work, it's a bug. HTH Oliver