From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Subject: Re: [PATCH tty-next 14/22] tty: Remove tty_wait_until_sent_from_close() Date: Tue, 17 Jun 2014 07:32:15 -0400 Message-ID: <53A0273F.70400@hurleysoftware.com> References: <1402924639-5164-1-git-send-email-peter@hurleysoftware.com> <1402924639-5164-15-git-send-email-peter@hurleysoftware.com> <4575870.N9RCpZ4UMg@wuerfel> <53A01F02.7000202@hurleysoftware.com> <063D6719AE5E284EB5DD2968C1650D6D1725DAF6@AcuExch.aculab.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mailout32.mail01.mtsvc.net ([216.70.64.70]:50156 "EHLO n23.mail01.mtsvc.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754281AbaFQLcT (ORCPT ); Tue, 17 Jun 2014 07:32:19 -0400 In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D1725DAF6@AcuExch.aculab.com> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: David Laight , Arnd Bergmann Cc: "linuxppc-dev@lists.ozlabs.org" , Greg Kroah-Hartman , Karsten Keil , "linux-kernel@vger.kernel.org" , "linux-serial@vger.kernel.org" , One Thousand Gnomes On 06/17/2014 07:03 AM, David Laight wrote: > From: Peter Hurley > ... >>> I don't understand the second half of the changelog, it doesn't seem >>> to fit here: there deadlock that we are trying to avoid here happens >>> when the *same* tty needs the lock to complete the function that >>> sends the pending data. I don't think we do still do that any more, >>> but it doesn't seem related to the tty lock being system-wide or not. >> >> The tty lock is not used in the i/o path; it's purpose is to >> mutually exclude state changes in open(), close() and hangup(). >> >> The commit that added this [1] comments that _other_ ttys may wait >> for this tty to complete, and comments in the code note that this >> function should be removed when the system-wide tty mutex was removed >> (which happened with the commit noted in the changelog). > > What happens if another process tries to do a non-blocking open > while you are sleeping in close waiting for output to drain? > > Hopefully this returns before that data has drained. Good point. tty_open() should be trylocking both mutexes anyway in O_NONBLOCK. Regards, Peter Hurley