linux-kernel - Re: Possible Oprofile crash/race when stopping

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Message-ID: <20100728122111.GO26154@erda.amd.com>
Date:	Wed, 28 Jul 2010 14:21:11 +0200
From:	Robert Richter <robert.richter@....com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Carl E. Love" <cel@...ibm.com>,
	Michael Ellerman <michaele@....ibm.com>
Subject: Re: Possible Oprofile crash/race when stopping

On 22.07.10 01:14:40, Benjamin Herrenschmidt wrote:
> Hi folks !
> 
> We've hit a strange crash internally, that we -think- we have tracked
> down to an oprofile bug. It's hard to hit, so I can't guarantee yet that
> we have fully smashed it but I'd like to share our findings in case you
> guys have a better idea.
> 
> So the initial observation is a spinlock bad magic followed by a crash
> in the spinlock debug code:

Benjamin,

thanks for reporting this. I was trying to reproduce this with various
loads and scenarios, but without success so far. Can you give me a
hint of the load you have (number of processes running, cpu load, do
you switch off oprofile while many processes are still running)? Are
you able to regularly trigger it?

> I think the right sequence however requires breaking up end_sync. Ie, we
> need to do in that order:
> 
>   - cancel the workqueues
>   - unregister the notifier
>   - process the mortuary
> 
> What do you think ?

This could potentially fix it, I will have to look deeper into the
code. Try to do this next week.

Thanks,

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center

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