From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756614AbaH0BhE (ORCPT ); Tue, 26 Aug 2014 21:37:04 -0400 Received: from cn.fujitsu.com ([59.151.112.132]:3632 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1752295AbaH0BhB convert rfc822-to-8bit (ORCPT ); Tue, 26 Aug 2014 21:37:01 -0400 X-IronPort-AV: E=Sophos;i="5.04,408,1406563200"; d="scan'208";a="35115377" Message-ID: <53FD356D.6050507@cn.fujitsu.com> Date: Wed, 27 Aug 2014 09:33:33 +0800 From: Chai Wen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0) Gecko/20110812 Thunderbird/6.0 MIME-Version: 1.0 To: Don Zickus CC: , , Subject: Re: [PATCH] softlockup: make detector be aware of task switch of processes hogging cpu References: <20140821023051.GO49576@redhat.com> <1408599742-21674-1-git-send-email-chaiw.fnst@cn.fujitsu.com> <20140822015822.GZ49576@redhat.com> <53FC82D2.1020401@cn.fujitsu.com> <20140826142214.GN49576@redhat.com> In-Reply-To: <20140826142214.GN49576@redhat.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Originating-IP: [10.167.226.161] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/26/2014 10:22 PM, Don Zickus wrote: > On Tue, Aug 26, 2014 at 08:51:30PM +0800, Chai Wen wrote: >> On 08/22/2014 09:58 AM, Don Zickus wrote: >> >>> On Thu, Aug 21, 2014 at 01:42:22PM +0800, chai wen wrote: >>>> For now, soft lockup detector warns once for each case of process softlockup. >>>> But the thread 'watchdog/n' may not always get the cpu at the time slot between >>>> the task switch of two processes hogging that cpu to reset soft_watchdog_warn. >>>> >>>> An example would be two processes hogging the cpu. Process A causes the >>>> softlockup warning and is killed manually by a user. Process B immediately >>>> becomes the new process hogging the cpu preventing the softlockup code from >>>> resetting the soft_watchdog_warn variable. >>>> >>>> This case is a false negative of "warn only once for a process", as there may >>>> be a different process that is going to hog the cpu. Resolve this by >>>> saving/checking the task pointer of the hogging process and use that to reset >>>> soft_watchdog_warn too. >>>> >>>> Signed-off-by: chai wen >>>> Signed-off-by: Don Zickus >>> >>> Acked-by: Don Zickus >>> >> >> >> Hi Andrew >> >> Sorry for some disturbing. >> Could you help to check and pick up this little improvement patch ? >> >> I am not sure which MAINTAINER I should talk to, but the original version of >> this patch is queued to -mm tree by you, so I assume that they are in the charge of you. >> >> >> thanks >> chai wen > > Hi Chai, > > Sorry about that. Ingo asked me privately to pick this up and re-post > with my signoff. I was converting to a new test env and was going to use this > patch as an excuse to exercise it. That is the delay. Let me get this > out today. > OK， It is kind of you to do that, thanks for your work. :) thanks chai wen > Cheers, > Don > >> >>>> --- >>>> kernel/watchdog.c | 16 +++++++++++++++- >>>> 1 files changed, 15 insertions(+), 1 deletions(-) >>>> >>>> diff --git a/kernel/watchdog.c b/kernel/watchdog.c >>>> index 0037db6..2e55620 100644 >>>> --- a/kernel/watchdog.c >>>> +++ b/kernel/watchdog.c >>>> @@ -42,6 +42,7 @@ static DEFINE_PER_CPU(bool, softlockup_touch_sync); >>>> static DEFINE_PER_CPU(bool, soft_watchdog_warn); >>>> static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts); >>>> static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt); >>>> +static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved); >>>> #ifdef CONFIG_HARDLOCKUP_DETECTOR >>>> static DEFINE_PER_CPU(bool, hard_watchdog_warn); >>>> static DEFINE_PER_CPU(bool, watchdog_nmi_touch); >>>> @@ -328,8 +329,20 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) >>>> return HRTIMER_RESTART; >>>> >>>> /* only warn once */ >>>> - if (__this_cpu_read(soft_watchdog_warn) == true) >>>> + if (__this_cpu_read(soft_watchdog_warn) == true) { >>>> + /* >>>> + * Handle the case where multiple processes are >>>> + * causing softlockups but the duration is small >>>> + * enough, the softlockup detector can not reset >>>> + * itself in time. Use task pointers to detect this. >>>> + */ >>>> + if (__this_cpu_read(softlockup_task_ptr_saved) != >>>> + current) { >>>> + __this_cpu_write(soft_watchdog_warn, false); >>>> + __touch_watchdog(); >>>> + } >>>> return HRTIMER_RESTART; >>>> + } >>>> >>>> if (softlockup_all_cpu_backtrace) { >>>> /* Prevent multiple soft-lockup reports if one cpu is already >>>> @@ -345,6 +358,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) >>>> pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n", >>>> smp_processor_id(), duration, >>>> current->comm, task_pid_nr(current)); >>>> + __this_cpu_write(softlockup_task_ptr_saved, current); >>>> print_modules(); >>>> print_irqtrace_events(current); >>>> if (regs) >>>> -- >>>> 1.7.1 >>>> >>> . >>> >> >> >> >> -- >> Regards >> >> Chai Wen > . > -- Regards Chai Wen