Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759653Ab3CGRzV (ORCPT ); Thu, 7 Mar 2013 12:55:21 -0500 Received: from mx1.redhat.com ([209.132.183.28]:42941 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756093Ab3CGRzT (ORCPT ); Thu, 7 Mar 2013 12:55:19 -0500 Date: Thu, 7 Mar 2013 18:53:05 +0100 From: Oleg Nesterov To: Henrique de Moraes Holschuh Cc: Mandeep Singh Baines , Linux Kernel Mailing List , linux-acpi@vger.kernel.org, ibm-acpi@hmh.eng.br, ibm-acpi-devel@lists.sourceforge.net, platform-driver-x86@vger.kernel.org, Aaron Lu , Tejun Heo , Andrew Morton Subject: [PATCH 0/1] thinkpad-acpi: kill hotkey_thread_mutex Message-ID: <20130307175305.GA15631@redhat.com> References: <201303042055.38040.maciej.rutecki@gmail.com> <1362504883-9180-1-git-send-email-msb@chromium.org> <20130305174838.GA7276@redhat.com> <20130305180542.GA12738@redhat.com> <20130305232603.GA16045@khazad-dum.debian.net> <20130306154420.GA7697@redhat.com> <20130306233232.GA12645@khazad-dum.debian.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130306233232.GA12645@khazad-dum.debian.net> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1824 Lines: 47 On 03/06, Henrique de Moraes Holschuh wrote: > > On Wed, 06 Mar 2013, Oleg Nesterov wrote: > > > > static void hotkey_poll_stop_sync(void) > > { > > if (tpacpi_hotkey_task) { > > kthread_stop(tpacpi_hotkey_task); > > tpacpi_hotkey_task = NULL; > > mutex_lock(&hotkey_thread_mutex); > > /* at this point, the thread did exit */ > > mutex_unlock(&hotkey_thread_mutex); > > } > > } > > > > And I simply do not understand the comment. This thread has already exited > > when kthread_stop() returns (OK, it can be running do_exit() paths but this > > doesn't matter). So this mutex_lock() buys nothing afaics. > > It was added due to an oops, waaaaay back then. If it is not needed > anymore, and there is zero chance of the kthread still being active when > hotkey_poll_stop_sync() ends, hotkey_thread_mutex can be simply removed. Well, there could be another bug. Say, hotkey_poll_stop_sync() can block on hotkey_thread_mutex if another thread was started. But at first glance this can't happen (hotkey_mutex), and even _if_ it can this needs another fix. > Looks like it, if the current semanthics of ktread_stop() are syncronous. IIRC, it always was... But at least currently it is certainly syncronous. kthread_stop(t) does wait_for_completion(t->vfork_done), complete(vfork_done) can't happen unless this task calls do_exit(). Hmm. I just noticed that the recent changes in kthread_stop() are not correct... But this is offtopic and doesn't affect thinkpad_acpi.c, I'll write another email later. So, what do you think about (UNTESTED) 1/1 ? Oleg. -- 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/