Messages in this thread | | | Date | Mon, 21 May 2018 17:07:34 -0700 | From | Joel Fernandes <> | Subject | Re: [PATCH v3 4/4] rcu: Unlock non-start node only after accessing its gp_seq_needed |
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On Mon, May 21, 2018 at 04:25:38PM -0700, Paul E. McKenney wrote: > On Sun, May 20, 2018 at 09:42:20PM -0700, Joel Fernandes wrote: > > We acquire gp_seq_needed locklessly. To be safe, lets do the unlocking > > after the access. > > Actually, no, we hold rnp_start's ->lock throughout. And this CPU (or in > the case of no-CBs CPUs, this task) is in charge of rdp->gp_seq_needed, > so nothing else is accessing it. Or at least that is the intent. ;-)
I was talking about protecting the internal node's rnp->gp_seq_needed, not the rnp_start's gp_seq_needed.
We are protecting them in the loop:
like this: for(...) if (rnp != rnp_start) raw_spin_lock_rcu_node(rnp); [...] // access rnp->gp_seq and rnp->gp_seq_needed [...] if (rnp != rnp_start) raw_spin_unlock_rcu_node(rnp);
But we don't need to do such protection in unlock_out ? I'm sorry if I'm missing something, but I'm wondering if rnp->gp_seq_needed of an internal node can be accessed locklessly, then why can't that be done also in the funnel locking loop - after all we are holding the rnp_start's lock through out right?
thanks!
- Joel
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