Messages in this thread | | | Date | Mon, 25 Oct 2010 18:03:43 +0200 | From | Tejun Heo <> | Subject | Re: Question about synchronize_sched_expedited() |
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Hello, Paul.
On 10/25/2010 05:43 PM, Paul E. McKenney wrote: > Hello, Tejun, > > I was taking another look at synchronize_sched_expedited(), and was > concerned about the scenario listed out in the following commit. > Is this scenario a real problem, or am I missing the synchronization > that makes it safe? > > (If my concerns are valid, I should also be able to change this > to non-atomically increment synchronize_sched_expedited_count, but > one step at a time...)
I think your concern is valid and this can happen w/o preemption given enough cpus and perfect timing. Was the original code free from this problem?
IMHO the counter based mechanism is a bit too difficult to ponder and verify. Can we do more conventional double queueing (ie. flipping pending and executing queues so that multiple sync calls can get coalesced while another one is in progress)? That's what the code is trying to achieve anyway, right?
Thanks.
-- tejun
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