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Date: Fri, 28 Mar 2003 17:05:53 +0100
To: Ingo Molnar <mingo@elte.hu>
From: Mike Galbraith <efault@gmx.de>
Subject: Re: 2.5.66-mm1
Cc: Zwane Mwaikambo <zwane@linuxpower.ca>, Andrew Morton <akpm@digeo.com>,
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At 04:25 PM 3/28/2003 +0100, Ingo Molnar wrote:

>On Fri, 28 Mar 2003, Zwane Mwaikambo wrote:
>
> > Hmm i think i may have his this one but i never posted due to being
> > unable to reproduce it on a vanilla kernel or the same kernel afterwards
> > (which was hacked so i won't vouch for it's cleanliness). I think
> > preempt might have bitten him in a bad place (mine is also
> > CONFIG_PREEMPT), is it possible that when we did the task_rq_unlock we
> > got preempted and when we got back we used the local variable
> > requeue_waker which was set before dropping the lock, and therefore
> > might not be valid anymore due to scheduler decisions done after
> > dropping the runqueue lock?
>
>yes, this one was my only suspect, but it should really never cause any
>problems. We might change sleep_avg during the wakeup, and carry the
>requeue_waker flag over a preemptible window, but the requeueing itself
>re-takes the runqueue lock, and does not take anything for granted. The
>flag could very well be random as well, and the code should still be
>correct - there's no requirement to recalculate the priority every time we
>change sleep_avg. (in fact we at times intentionally keep those values
>detached.)

In my 66-twiddle tree, I moved that under the lock out of pure paranoia.  I 
can try to see if printing under hefty (very) load will still trigger the 
occasional explosion.

         -Mike 

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