From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH tty-next 14/22] tty: Remove tty_wait_until_sent_from_close() Date: Tue, 17 Jun 2014 13:31:38 +0200 Message-ID: <8191805.dfI4LbYmWz@wuerfel> References: <1402924639-5164-1-git-send-email-peter@hurleysoftware.com> <53A01F02.7000202@hurleysoftware.com> <063D6719AE5E284EB5DD2968C1650D6D1725DAF6@AcuExch.aculab.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: Received: from mout.kundenserver.de ([212.227.17.10]:49942 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754870AbaFQLbw (ORCPT ); Tue, 17 Jun 2014 07:31:52 -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 Cc: 'Peter Hurley' , "linuxppc-dev@lists.ozlabs.org" , Greg Kroah-Hartman , Karsten Keil , "linux-kernel@vger.kernel.org" , "linux-serial@vger.kernel.org" , One Thousand Gnomes On Tuesday 17 June 2014 11:03:50 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. Before the patch, I believe tty_reopen() would return -EIO because the TTY_CLOSING flag is set. After the patch, tty_open() blocks on tty_lock() before calling tty_reopen(). AFAICT, this is independent of O_NONBLOCK. Arnd