linux-kernel - Re: [PATCH v3 0/3] qrwlock: Introducing a queue read/write lock implementation

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Message-ID: <520BA109.1000501@hp.com>
Date:	Wed, 14 Aug 2013 11:23:53 -0400
From:	Waiman Long <waiman.long@...com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Matt Fleming <matt.fleming@...el.com>,
	Michel Lespinasse <walken@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	Rik van Riel <riel@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	George Spelvin <linux@...izon.com>,
	Harvey Harrison <harvey.harrison@...il.com>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH v3 0/3] qrwlock: Introducing a queue read/write lock implementation

On 08/14/2013 06:20 AM, Ingo Molnar wrote:
> * Waiman Long<waiman.long@...com>  wrote:
>
>>
>> I would like to share with you a rwlock related system crash that I
>> encountered during my testing with hackbench on an 80-core DL980. The
>> kernel crash because of a "watchdog detected hard lockup on cpu 79". The
>> crashing CPU was running "write_lock_irq(&tasklist_lock)" in
>> forget_original_parent() of the exit code path when I interrupted the
>> hackbench which was spawning thousands of processes. Apparently, the
>> remote CPU was not able to get the lock for a sufficient long time due
>> to the unfairness of the rwlock which I think my version of queue rwlock
>> will be able to alleviate this issue.
>>
>> So far, I was not able to reproduce the crash. I will try to see if I
>> could more consistently reproduce it.
> Was it an actual crash/lockup, or a longish hang followed by a lock
> detector splat followed by the system eventually recovering back to
> working order?
>
> Thanks,
>
> 	Ingo

It was an actual crash initiated by the NMI handler. I think the system 
was in a halt state after that.

Regards,
Longman
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