linux-kernel - Re: [BUG] 2.6.23-git8 kernel oops at __rb_rotate

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Message-ID: <20071017145226.GA21676@elte.hu>
Date:	Wed, 17 Oct 2007 16:52:26 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Cc:	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	torvalds@...ux-foundation.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Whitcroft <apw@...dowen.org>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Mike Galbraith <efault@....de>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>
Subject: Re: [BUG] 2.6.23-git8 kernel oops at __rb_rotate_left+0x7/0x70


* Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com> wrote:

> On Wed, Oct 17, 2007 at 04:21:40PM +0200, Ingo Molnar wrote:
> > * Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com> wrote:
> > 
> > > While running kernbench with the 2.6.23-git8 following oops is 
> > > produced
> > 
> > Dmitry found something that might explain the crash: could you check 
> > whether the patch below fixes it?
> 
> > this should fix the put_prev_task crashes that were reported,
> > Dmitry Adamushko noticed that it's not valid to call into
> > task_new_fair() if this_cpu != task_cpu(p).
> 
> I don't see a fundamental reason why it would be invalid to call 
> task_new_fair() when this_cpu != task_cpu(p). Besides, calling 
> activate_task->enqueue_task->enqueue_task_fair() on a new born task 
> (as is being done in the patch you have sent) is slightly buggy in the 
> sense that its p->se.vruntime is not properly calculated (because we 
> set wakeup argument as 0).

yes - i pointed this out in a separate mail.

> We (myself, Kamalesh and Dhaval) have tested the patch below, w/o 
> being able to recreate the problem. The patch allows for 
> task_new_fair() to be called even for the case when child is being 
> added to another cpu's runqueue.

yes, and your fix is the better one, it goes into the next batch of 
fixes.

	Ingo
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