From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758780AbaHZOWV (ORCPT ); Tue, 26 Aug 2014 10:22:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34584 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758374AbaHZOWS (ORCPT ); Tue, 26 Aug 2014 10:22:18 -0400 Date: Tue, 26 Aug 2014 10:22:14 -0400 From: Don Zickus To: Chai Wen Cc: akpm@linux-foundation.org, mingo@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] softlockup: make detector be aware of task switch of processes hogging cpu Message-ID: <20140826142214.GN49576@redhat.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53FC82D2.1020401@cn.fujitsu.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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