Messages in this thread | | | Date | Wed, 21 Jul 2004 22:35:25 +0200 | From | Manfred Spraul <> | Subject | Re: [Lse-tech] [RFC, PATCH] 5/5 rcu lock update: Hierarchical rcu_cpu_mask bitmap |
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Paul E. McKenney wrote:
>I don't understand how the following helps, given that the CPU being >offlined is supposed to be completely dead by the time we get here. >Can't see anything that it really hurts other than a bit of delay in >an extremely infrequent operation, but... > > > >>+ spin_unlock_wait(&rcu_state.mutex); >> cpu_quiet(cpu, 1); >> >>
I was concerned about a race of cpu_quiet for the dead cpu (last cpu in a group) with a concurrent cpu_quiet for another cpu in another cpu group. A stale bit in either rcu_state.outstanding or rcu_groups[].outstanding would lock up the rcu subsystem. I've thought about it again and I agree with you - there is no race.
I agree with most of your other points - the patch is a proof of concept, it definitively needs a big cleanup before is should be considered for merging [+ a system that needs it]
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