linux-kernel - Re: [lkp] [fs] df4c0e36f1: NMI watchdog: BUG: soft lockup

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Message-ID: <5637C288.9070508@intel.com>
Date:	Mon, 2 Nov 2015 12:07:36 -0800
From:	Dave Hansen <dave.hansen@...el.com>
To:	Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc:	kernel test robot <ying.huang@...ux.intel.com>, LKP <lkp@...org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Christoph Lameter <cl@...ux.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Yuri Gribov <tetra2005@...il.com>,
	Andrey Konovalov <adech.fo@...il.com>,
	Konstantin Serebryany <kcc@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [lkp] [fs] df4c0e36f1: NMI watchdog: BUG: soft lockup - CPU#0
 stuck for 22s! [swapper/0:1]

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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