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Date: Wed, 14 Aug 2013 11:23:53 -0400
From: Waiman Long <waiman.long@hp.com>
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To: Ingo Molnar <mingo@kernel.org>
CC: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Arnd Bergmann <arnd@arndb.de>,
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        Steven Rostedt <rostedt@goodmis.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Matt Fleming <matt.fleming@intel.com>,
        Michel Lespinasse <walken@google.com>,
        Andi Kleen <andi@firstfloor.org>, Rik van Riel <riel@redhat.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        George Spelvin <linux@horizon.com>,
        Harvey Harrison <harvey.harrison@gmail.com>,
        "Chandramouleeswaran, Aswin" <aswin@hp.com>,
        "Norton, Scott J" <scott.norton@hp.com>
Subject: Re: [PATCH v3 0/3] qrwlock: Introducing a queue read/write lock implementation
References: <1375315259-29392-1-git-send-email-Waiman.Long@hp.com> <520A811A.7080907@hp.com> <20130814102041.GG10849@gmail.com>
In-Reply-To: <20130814102041.GG10849@gmail.com>
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On 08/14/2013 06:20 AM, Ingo Molnar wrote:
> * Waiman Long<waiman.long@hp.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