Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755712AbaFQITT (ORCPT ); Tue, 17 Jun 2014 04:19:19 -0400 Received: from mx0.aculab.com ([213.249.233.131]:44097 "HELO mx0.aculab.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752816AbaFQITQ (ORCPT ); Tue, 17 Jun 2014 04:19:16 -0400 From: David Laight To: "'Arnd Bergmann'" , "linuxppc-dev@lists.ozlabs.org" CC: One Thousand Gnomes , Karsten Keil , Peter Hurley , "Greg Kroah-Hartman" , "linux-kernel@vger.kernel.org" , "linux-serial@vger.kernel.org" Subject: RE: [PATCH tty-next 14/22] tty: Remove tty_wait_until_sent_from_close() Thread-Topic: [PATCH tty-next 14/22] tty: Remove tty_wait_until_sent_from_close() Thread-Index: AQHPigK/wgSnyL5/CECAg051obYgppt09HQw Date: Tue, 17 Jun 2014 08:18:03 +0000 Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1725D868@AcuExch.aculab.com> References: <1402924639-5164-1-git-send-email-peter@hurleysoftware.com> <1402924639-5164-15-git-send-email-peter@hurleysoftware.com> <4575870.N9RCpZ4UMg@wuerfel> In-Reply-To: <4575870.N9RCpZ4UMg@wuerfel> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.202.99.200] Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by mail.home.local id s5H8JPoT005417 From: Arnd Bergmann > On Monday 16 June 2014 09:17:11 Peter Hurley wrote: > > tty_wait_until_sent_from_close() drops the tty lock while waiting > > for the tty driver to finish sending previously accepted data (ie., > > data remaining in its write buffer and transmit fifo). > > > > However, dropping the tty lock is a hold-over from when the tty > > lock was system-wide; ie., one lock for all ttys. > > > > Since commit 89c8d91e31f267703e365593f6bfebb9f6d2ad01, > > 'tty: localise the lock', dropping the tty lock has not been necessary. > > > > CC: Karsten Keil > > CC: linuxppc-dev@lists.ozlabs.org > > Signed-off-by: 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. While I've not looked at the code in question; my thoughts were that holding any lock while waiting for output to drain (or anything else really) probably isn't a good idea. You might find that something else needs the lock - even if only some kind of status request. David ????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m???? ????????I?