Subject: Re: [lkp] [fs] df4c0e36f1: NMI watchdog: BUG: soft lockup - CPU#0
 stuck for 22s! [swapper/0:1]
To: Andrey Ryabinin <ryabinin.a.a@gmail.com>
References: <87611kakr3.fsf@yhuang-dev.intel.com>
 <CAPAsAGwVYSgXm0Rgbtim-5iFxhWaakc1emXQALKwYLm36OoVsw@mail.gmail.com>
 <56379FDE.6010603@intel.com>
 <CAPAsAGzpTM84NEESPt_jY0i-+W2SB37KtW1TXy93e8R2F7rEtw@mail.gmail.com>
Cc: kernel test robot <ying.huang@linux.intel.com>, LKP <lkp@01.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Rientjes <rientjes@google.com>,
        Pekka Enberg <penberg@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
        Andi Kleen <andi@firstfloor.org>, Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Christoph Lameter <cl@linux.com>, Sasha Levin <sasha.levin@oracle.com>,
        Konstantin Khlebnikov <koct9i@gmail.com>,
        Yuri Gribov <tetra2005@gmail.com>,
        Andrey Konovalov <adech.fo@gmail.com>,
        Konstantin Serebryany <kcc@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
From: Dave Hansen <dave.hansen@intel.com>
Message-ID: <5637C288.9070508@intel.com>
Date: Mon, 2 Nov 2015 12:07:36 -0800
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On 11/02/2015 11:34 AM, Andrey Ryabinin wrote:
>>> >>
>>> >> [    1.159450] augmented rbtree testing -> 23675 cycles
>>> >> [    1.864996]
>>> >> It took less than a second, meanwhile in your case it didn't finish in
>>> >> 22 seconds.
>>> >>
>>> >> This makes me think that your host is overloaded and the problem is on
>>> >> your side.
>> >
>> > It's probably just a matter of putting some cond_resched()s in the test
>> > code.
> Yes, but is it worthwhile? It's very likely that lockup will just
> trigger in another place.

I'm guessing that the lockup here was because the tests were running for
too long.  If we cond_resched() in there often enough, the kernel won't
detect a softlockup at all.  It won't shift somewhere else.
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