Messages in this thread | | | Date | Wed, 17 Nov 2004 09:49:31 +1100 | From | Nick Piggin <> | Subject | Re: [patch, 2.6.10-rc2] sched: fix ->nr_uninterruptible handling bugs |
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Ingo Molnar wrote: > PREEMPT_RT on SMP systems triggered weird (very high) load average > values rather easily, which turned out to be a mainline kernel > ->nr_uninterruptible handling bug in try_to_wake_up(). > > the following code: > > if (old_state == TASK_UNINTERRUPTIBLE) { > old_rq->nr_uninterruptible--; > > potentially executes with old_rq potentially being != rq, and hence > updating ->nr_uninterruptible without the lock held. Given a > sufficiently concurrent preemption workload the count can get out of > whack and updates might get lost, permanently skewing the global count. > Nothing except the load-average uses nr_uninterruptible() so this > condition can go unnoticed quite easily. >
Hi Ingo, Yes you're right.
I have another idea. Revert back to the old code, then just transfer the nr_uninterruptible count when migrating a task. That way, the rq's nr_uninterruptible field always is a measure of the number of uninterruptible tasks on it. What do you think?
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