From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751501AbbI2Xak (ORCPT ); Tue, 29 Sep 2015 19:30:40 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:45121 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750813AbbI2Xah (ORCPT ); Tue, 29 Sep 2015 19:30:37 -0400 Date: Tue, 29 Sep 2015 16:30:36 -0700 From: Andrew Morton To: Ulrich Obergfell Cc: linux-kernel@vger.kernel.org, dzickus@redhat.com, atomlin@redhat.com Subject: Re: [PATCH 0/5] improve handling of errors returned by kthread_park() Message-Id: <20150929163036.a1260608ab9b13273eebf9cb@linux-foundation.org> In-Reply-To: <1443473052-3053-1-git-send-email-uobergfe@redhat.com> References: <1443473052-3053-1-git-send-email-uobergfe@redhat.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 28 Sep 2015 22:44:07 +0200 Ulrich Obergfell wrote: > The original watchdog_park_threads() function that was introduced by > commit 81a4beef91ba4a9e8ad6054ca9933dff7e25ff28 takes a very simple > approach to handle errors returned by kthread_park(): It attempts to > roll back all watchdog threads to the unparked state. However, this > may be undesired behaviour from the perspective of the caller which > may want to handle errors as appropriate in its specific context. > Currently, there are two possible call chains: > > - watchdog suspend/resume interface > > lockup_detector_suspend > watchdog_park_threads > > - write to parameters in /proc/sys/kernel > > proc_watchdog_update > watchdog_enable_all_cpus > update_watchdog_all_cpus > watchdog_park_threads > > Instead of 'blindly' attempting to unpark the watchdog threads if a > kthread_park() call fails, the new approach is to disable the lockup > detectors in the above call chains. Failure becomes visible to the > user as follows: > > - error messages from lockup_detector_suspend() > or watchdog_enable_all_cpus() > > - the state that can be read from /proc/sys/kernel/watchdog_enabled > > - the 'write' system call in the latter call chain returns an error > hm, you made me look at kthread parking. Why does it exist? What is a "parked" thread anyway, and how does it differ from, say, a sleeping one? The 2a1d446019f9a5983ec5a335b changelog is pretty useless and the patch added no useful documentation, sigh. Anwyay... what inspired this patchset? Are you experiencing kthread_park() failures in practice? If so, what is causing them? And what is the user-visible effect of these failures? This is all pretty important context for such a patchset.