From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757803AbaHZMy4 (ORCPT ); Tue, 26 Aug 2014 08:54:56 -0400 Received: from cn.fujitsu.com ([59.151.112.132]:62150 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1754675AbaHZMyz (ORCPT ); Tue, 26 Aug 2014 08:54:55 -0400 X-IronPort-AV: E=Sophos;i="5.04,404,1406563200"; d="scan'208";a="35092577" Message-ID: <53FC82D2.1020401@cn.fujitsu.com> Date: Tue, 26 Aug 2014 20:51:30 +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: CC: Don Zickus , , 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> In-Reply-To: <20140822015822.GZ49576@redhat.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit 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 08/22/2014 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 >> --- >> 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