Messages in this thread | | | Subject | Re: lock order in O(1) scheduler | From | Robert Love <> | Date | 10 Jan 2002 00:51:03 -0500 |
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On Thu, 2002-01-10 at 00:10, kevin@koconnor.net wrote:
> I was unable to figure out what the logic of the '(smp_processor_id() < > p->cpu)' test is.. (Why should the CPU number of the process being awoken > matter?) My best guess is that this is to enforce a locking invariant - > but if so, isn't this test backwards? If p->cpu > current->cpu then > p->cpu's runqueue is locked first followed by this_rq - locking greatest to > least, where the rest of the code does least to greatest..
OK, I replied I was unsure of the validity, but looking this over, I now suspect it is wrong.
The test should be (smp_processor_id() > p->cpu). Thus it would be safe to lock this_rq since it is of a lower cpu id than p's rq.
Robert Love
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