From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753398AbdK0Swj (ORCPT ); Mon, 27 Nov 2017 13:52:39 -0500 Received: from out0-218.mail.aliyun.com ([140.205.0.218]:40912 "EHLO out0-218.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752868AbdK0Swc (ORCPT ); Mon, 27 Nov 2017 13:52:32 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R101e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e02c03271;MF=yang.s@alibaba-inc.com;NM=1;PH=DS;RN=3;SR=0;TI=SMTPD_---.9WXSr5f_1511808740; Subject: Re: [RFC PATCH 2/2] lib: debugobjects: touch watchdog to avoid softlockup when !CONFIG_PREEMPT To: Waiman Long , tglx@linutronix.de Cc: linux-kernel@vger.kernel.org References: <1510947833-116482-1-git-send-email-yang.s@alibaba-inc.com> <1510947833-116482-2-git-send-email-yang.s@alibaba-inc.com> <553877ed-843e-a59d-3a76-2e90ce192ab1@alibaba-inc.com> <1a6f92f5-2c12-1276-916b-fd2848899e5c@redhat.com> From: "Yang Shi" Message-ID: Date: Tue, 28 Nov 2017 02:52:19 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <1a6f92f5-2c12-1276-916b-fd2848899e5c@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/27/17 10:18 AM, Waiman Long wrote: > On 11/27/2017 12:54 PM, Yang Shi wrote: >> Hi Waiman, >> >> The second patch of this series. >> >> Thanks, >> Yang >> >> >> On 11/17/17 11:43 AM, Yang Shi wrote: >>> There are nested loops on debug objects free path, sometimes it may take >>> over hundred thousands of loops, then cause soft lockup with >>> !CONFIG_PREEMPT >>> occasionally, like below: >>> >>> ... >>> >>> The code path might be called in either atomic or non-atomic context, >>> so touching softlockup watchdog instead of calling cond_resched() which >>> might fall asleep. However, it is unnecessary to touch the watchdog >>> every loop, so just touch the watchdog at every 10000 (best estimate) >>> loops. >>> >>> Signed-off-by: Yang Shi > > I do have some concern about suppressing the soft lockup warning > entirely. If the system feels unresponsive for a certain period of time > (e.g. 22s), most users would like to know what is going on. It can be a > custom message with less scary warning. Alternatively, some opt-out I'm not sure if it is necessary for debug code since the unresponsiveness is introduced by debug config and is expected somehow, so the user is supposed to know what they are doing, and it sounds preferred to disregard the soft lockup message reported by object debug for the most time. We do have some other examples which suppress soft lockup completely in kernel, i.e. kdb debug, printing some verbose debug or error message, some slow driver code, etc. > mechanism can be added to explicitly disable soft lookup warning for > debugobjs is OK as long as it is not the default. If we really want to some opt-out, we should be able to add a proc knob to disable soft lockup as the patch does, but not default. If this is too overkilling, we may just add some comment in the Kconfig help text to tell users the side effect. Thanks, Yang > > Cheers, > Longman >