Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932236AbaFQK5P (ORCPT ); Tue, 17 Jun 2014 06:57:15 -0400 Received: from mailout32.mail01.mtsvc.net ([216.70.64.70]:44025 "EHLO n23.mail01.mtsvc.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755953AbaFQK5N (ORCPT ); Tue, 17 Jun 2014 06:57:13 -0400 Message-ID: <53A01F02.7000202@hurleysoftware.com> Date: Tue, 17 Jun 2014 06:57:06 -0400 From: Peter Hurley User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Arnd Bergmann , linuxppc-dev@lists.ozlabs.org CC: Greg Kroah-Hartman , One Thousand Gnomes , Karsten Keil , 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() 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> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated-User: 990527 peter@hurleysoftware.com X-MT-ID: 8FA290C2A27252AACF65DBC4A42F3CE3735FB2A4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/17/2014 04:00 AM, Arnd Bergmann wrote: > 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. 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). Regards, Peter Hurley [1] commit a57a7bf3fc7eff00f07eb9c805774d911a3f2472 Author: Jiri Slaby Date: Thu Aug 25 15:12:06 2011 +0200 TTY: define tty_wait_until_sent_from_close We need this helper to fix system stalls. The issue is that the rest of the system TTYs wait for us to finish waiting. This wasn't an issue with BKL. BKL used to unlock implicitly. This is based on the Arnd suggestion. Signed-off-by: Jiri Slaby Acked-by: Arnd Bergmann Signed-off-by: Greg Kroah-Hartman -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/